Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

In this study, we report the Doppler-free spectra ofbuffer-gas-cooledCaOH. We observed five Doppler-free spectra containing low-J Q(1) and R-12 transitions, which wereonly partially resolved by previous Doppler-limited spectroscopies.The spectra frequencies were corrected using the Doppler-free spectraof iodine molecules; accordingly, the uncertainty was estimated tobe below 10 MHz. We determined the spin-rotation constant inthe ground state, which agrees with the values reported in the literatureobtained based on millimeter-wave data within 1 MHz. This suggeststhat the relative uncertainty is much smaller. The present study demonstratesthe Doppler-free spectroscopy of a polyatomic radical and the broadapplicability of the buffer gas cooling method to molecular spectroscopy.CaOH is the only polyatomic molecule that can be directly laser-cooledand trapped in a magneto-optical trap. High-resolution spectroscopyof such molecules is useful for establishing efficient laser coolingschemes of polyatomic molecules.

DOI： 10.1021/acs.jpca.2c08565

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

Buffer-gas cooling is a universal cooling technique for molecules and used for various purposes. One of its ap- plications is using molecules inside a buffer-gas cell for low-temperature spectroscopy. Although a high-intensity signal is expected in the cell, complex molecular dynamics is a drawback for precise spectroscopy. In this study, we performed high-resolution absorption spectroscopy of low -J transitions in the A similar to 2 pi(0, 0, 0)-X similar to 2E+(0, 0, 0) band of calcium monohydroxide (CaOH). CaOH molecules were produced by laser ablation in a copper cell and cooled to similar to 5 K using helium buffer gas. We probed the Doppler effects in a buffer-gas cell by injecting counterpropagating lasers inside the cell. The time evolutions of the Doppler width and shift were simulated using a dedicated Monte Carlo simulation and compared with data.

DOI： 10.1103/PhysRevA.107.043114

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Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)  

For over five decades, studies in the field of chemical physics and physical chemistry have primarily aimed to understand the quantum properties of molecules. However, high-resolution rovibronic spectroscopy has been limited to relatively small and simple systems because translationally and rotationally cold samples have not been prepared in sufficiently large quantities for large and complex systems. In this study, we present high-resolution rovibronic spectroscopy results for large gas-phase molecules, namely, free-base phthalocya-nine (FBPc). The findings suggest that buffer-gas cooling may be effective for large molecules introduced via laser ablation. High-resolution electronic spectroscopy, combined with other experimental and theoretical studies, will be useful in understanding the quantum properties of molecules. These findings also serve as a guide for quantum chemical calculations of large molecules.

DOI： 10.1038/s42004-022-00783-4

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Publishing type：Research paper (scientific journal)  

High-resolution excitation spectra of the X0+→ A0+ and X0+→ C0+ transitions of lead monoxide (PbO) are observed in a range of 22 300-25 100 cm−1. Transition frequencies are determined with an average uncertainty of 8.5×10−4 cm−1 by comparing with resonances of an ultralow expansion etalon. PbO molecules are produced by laser ablation in a cold helium buffer gas, which provides rotationally cold but vibrationally hot molecules and allows observation of hot bands of excitation from the υ′′=1,2 vibrational states. Spectroscopic constants and potential curves for the A0+ and C0+ states are determined, and the spectroscopic constants obtained for the three main isotopologues are reproduced to a satisfactory level using a single potential curve for each electronic state. This indicates that perturbation due to other electronic states is negligibly small.

DOI： 10.1016/j.jms.2022.111713

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

Abstract

Calcium monohydroxide radical (CaOH) is receiving an increasing amount of attention from the astrophysics community as it is expected to be present in the atmospheres of hot rocky super-Earth exoplanets as well as interstellar and circumstellar environments. Here, we report the high-resolution laboratory absorption spectroscopy on low-J transitions in ${\tilde{A } }^{2}{\rm{\Pi } }(0,0,0)-{\tilde{X } }^{2}{ { \rm{\Sigma } } }^{+}(0,0,0)$ band of buffer-gas-cooled CaOH. In total, 40 transitions out of the low-J states were assigned, including 27 transitions that have not been reported in previous literature. The determined rotational constants for both ground and excited states are in excellent agreement with previous literature, and the measurement uncertainty for the absolute transition frequencies was improved by more than a factor of 3. This will aid future interstellar, circumstellar, and atmospheric identifications of CaOH. The buffer-gas-cooling method employed here is a particularly powerful method to probe low-J transitions and is easily applicable to other astrophysical molecules.

DOI： 10.3847/1538-4357/ac87fb

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Other Link： https://iopscience.iop.org/article/10.3847/1538-4357/ac87fb/pdf

Publishing type：Research paper (international conference proceedings)   Publisher：Journal of the Physical Society of Japan  

DOI： 10.7566/jpscp.33.011125

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Publishing type：Research paper (scientific journal)   Publisher：International Union of Crystallography (IUCr)  

This paper presents an absolute X-ray photon energy measurement method that uses a Bond diffractometer. The proposed system enables the prompt and rapid <italic>in situ</italic> measurement of photon energies over a wide energy range. The diffractometer uses a reference silicon single-crystal plate and a highly accurate angle encoder called SelfA. The performance of the system is evaluated by repeatedly measuring the energy of the first excited state of the potassium-40 nuclide. The excitation energy is determined as 29829.39 (6) eV, and this is one order of magnitude more accurate than the previous measurement. The estimated uncertainty of the photon energy measurement was 0.7 p.p.m. as a standard deviation and the maximum observed deviation was 2 p.p.m.

DOI： 10.1107/s1600577520014526

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：{IOP} Publishing  

We study nearly degenerate four-wave mixing using a two-photon-allowed vibrational transition of parahydrogen. A signal photon is generated by a trigger photon and coherence among parahydrogen, which is prepared by two counterpropagating pump pulses, and we investigate the dependence of the signal pulse energy on the trigger frequency. The measured spectra depend on the geometry, shifting depending on the direction of the signal pulse and on the small angle formed by the counterpropagating pump pulses. Furthermore, we investigate the dependence of signal pulse energy on the incident time of the trigger pulse. The measured signal pulse energy is high if the trigger pulse is delayed slightly with respect to the pump pulses. We demonstrate that these geometry-dependent spectra and coherent-transient response can be explained by using simple models.

DOI： 10.1088/1361-6455/ab4a6e

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1038/s41586-019-1542-3

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：{IOP} Publishing  

We observed two-photon emission (TPE) signal from the first vibrationally excited state of parahydrogen gas coherently excited by counter-propagating laser pulses. A single narrow-linewidth laser source has roles in the excitation of the parahydrogen molecules and the induction of the TPE process. We measured dependences of the signal energy on the detuning, target gas pressure, and input pulse energies. These results are qualitatively consistent with those obtained by numerical simulations based on Maxwell-Bloch equations with one spatial dimension and one temporal dimension. This study of the TPE process in the counterpropagating injection scheme is an important step toward neutrino mass spectroscopy.

DOI： 10.1088/1361-6455/aafbd0

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

This paper reports on the demonstration of a high-rate energy measurement technique using a thin depletion layer silicon avalanche photodiode (Si-APD). A dedicated amplitude-to-time converter is developed to realize simultaneous energy and timing measurement in a high rate condition. The energy response of the system is systematically studied by using monochromatic X-ray beam with an incident energy ranging from 6 to 33 keV. The obtained energy spectra contain clear peaks and tail distributions. The peak fraction monotonously decreases as the incident photon energy increases. This phenomenon can be explained by considering the distribution of the energy deposit in silicon, which is investigated by using a Monte Carlo simulation.

DOI： 10.1016/j.nima.2018.10.029

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：{IOP} Publishing  

We report the coherent excitation of the vibrational state of hydrogen molecules by two-photon absorption and the resultant third-harmonic generation (THG). Parahydrogen molecules cooled by liquid nitrogen are irradiated by mid-infrared nanosecond pulses at 4.8 mu m with a nearly Fourier-transform-limited linewidth. The first excited vibrational state of parahydrogen is populated by two-photon absorption of the mid-infrared photons. Because of the narrow linewidth of the mid-infrared pulses, coherence between the ground and excited states is sufficient to induce higher-order processes. Near-infrared photons from the THG are observed at 1.6 mu m. The dependence of the intensity of the near-infrared radiation on mid-infrared pulse energy, target pressure, and cell length is determined. We used a simple formula for THG with consideration of realistic experimental conditions to explain the observed results.

DOI： 10.1088/1361-6455/aa9782

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier B.V.  

Optical free induction decay (FID) signals of the CH3F ν4 band were observed by using a cw-OPO infrared laser coupled with a Stark switching method. The observed signals have been Fourier transformed to obtain the Lorentz functions and the widths have been analyzed to determine the pressure-broadening coefficients for rR(0,0), rQ(1,0), rR(1,0), rR(1,1), and pP(2,1) to be 1/(πT2 p) = (46.1 ± 2.1), (31.6 ± 3.6), (21.8 ± 2.5), (25.2 ± 4.0), and (26.5 ± 1.8) MHz/Torr, where T2 is the transverse decay time. The value of rR(0,0) is larger than that determined from a recent pressure-broadening measurement by 39 ± 12%. The difference is explained by collision induced reorienting transitions (ΔM = ±1, ΔJ = 0).

DOI： 10.1016/j.cplett.2017.12.009

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

Nuclear resonant excitation and detection of its decay signal for the 26.27-keV level of Hg201 is demonstrated with high-brilliance synchrotron radiation (SR) and a fast x-ray detector system. This SR-based photonuclear excitation scheme, known as nuclear resonant scattering (NRS) in the field of materials science, is also useful for investigating nuclear properties, such as the half-lives and radiative widths of excited nuclear levels. To date, because of the limited time response of the x-ray detector, the nuclear levels to which this method could be applied have been limited to the one whose half-lives are longer than ∼1 ns. The faster time response of the NRS measurement makes possible NRS experiments on nuclear levels with much shorter half-lives. We have fabricated an x-ray detector system that has a time resolution of 56 ps and a shorter tail function than that reported previously. With the implemented detector system, the NRS signal of the 26.27-keV state of Hg201 could be clearly discriminated from the electronic scattering signal at an elapsed time of 1 ns after the SR pulse. The half-life of the state was determined as 629 ± 18 ps, which has better precision by a factor of three compared with that reported to date obtained from nuclear decay spectroscopy.

DOI： 10.1103/PhysRevC.97.024607

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society ({ACS})  

We report the observation of two-photon emission from a coherently excited vibrational state of solid parahydrogen, which is also a known quantum solid. Coherence between the ground and the excited states is prepared by stimulated Raman scattering using two visible laser pulses. The two-photon emission is triggered by another mid-infrared laser pulse. It was observed that the two-photon emission persists even when the trigger pulse is injected long after the excitation. This is due to the long decoherence time of the vibrational states of solid parahydrogen. It is found that the emission intensity increases even after the excitation pulses pass through the target completely. This coherence development is highly suppressed at high target temperatures and high residual orthohydrogen concentrations. Effects of target annealing and laser-induced damage on the target are also observed.

DOI： 10.1021/acs.jpca.7b02011

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

The bleaching process in the C-F stretching mode (v(3) band) of CH3F-(ortho-H-2)(n) [n = 0 and 1] clusters in solid para-H-2 was monitored using pump and probe laser spectroscopy on the C-H stretching mode (v(1) and 2v(5) bands). From an analysis of the depleted spectral profiles, the transition frequency and linewidth of each cluster were directly determined. The results agree with the values previously derived from a deconvolution analysis of the broadened v(1)/2v(5) spectrum observed by FTIR spectroscopy. The complementary increase and decrease between the n = 0 and 1 components were also verified through monitoring the v(1) and 2v(5) bands, which suggests a closed system among the CH3F(ortho-H-2)(n) clusters. These observations provide experimental verification of the CH3F-(ortho-H-2)(n) cluster model. On the other hand, a trial to observe the bleaching process by pumping the C-H stretching mode was not successful. This result may be important for understanding the dynamics of vibrational relaxation processes in CH3F-(ortho-H-2) n in solid para-H-2. Published by AIP Publishing.

DOI： 10.1063/1.4978227

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We report on the generation of nanosecond mid-infrared pulses having frequency tunability, a narrow linewidth, and a high pulse energy. These pulses are obtained by frequency mixing between injection-seeded near-infrared pulses in potassium titanyl arsenate crystals. A continuous-wave external cavity laser diode or a Ti:sapphire ring laser is used as a tunable seeding source for the near-infrared pulses. The typical energy of the generated mid-infrared pulses is in the range of 0.4-1mJ/pulse. The tuning wavelength ranges from 3142 to 4806 nm. A narrow linewidth of 1.4GHz and good frequency reproducibility of the mid-infrared pulses are confirmed by observing a rovibrational absorption line of gaseous carbon monoxide at 4587 nm. (C) 2017 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.56.032101

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

We investigate how the efficiency of coherently amplified two-photon emission depends on the frequency of one of the two emitted photons, namely the signal photon. This is done over the wavelength range of 5.048-10.21 μm by using the vibrational transition of parahydrogen. The efficiency increases with the frequency of the signal photon. Considering experimental errors, our results are consistent with the theoretical prediction for the present experimental conditions. This study is an experimental demonstration of the frequency dependence of coherently amplified two-photon emission, and also presents its potential as a light source.

DOI： 10.1103/PhysRevA.96.063827

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Institute of Physics Inc.  

We developed a fast X-ray detector system for nuclear resonant scattering (NRS) experiments. Our system employs silicon avalanche photo-diode (Si-APD) as a fast X-ray sensor. The system is able to acquire both timing and energy of a single X-ray photon simultaneously in a high rate condition, 106 counts per second for one Si-APD. The performance of the system was investigated in SPring-8, a synchrotron radiation facility in Japan. Good time resolution of 120 ps (FWHM) was achieved with a slight tail distribution in the time spectrum by a level of 10-9 at 1 ns apart from the peak. Using this system, we successfully observed the NRS from the 26.27-keV level of mercury-201, which has a half-life of 630(50) ps. We also demonstrated the reduction of background events caused by radioactive decays in a radioactive sample by discriminating photon energy.

DOI： 10.1063/1.4989405

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

Previous experimental studies of superradiance (SR) in multi-level systems have been explainable using the predictions of the well-known simple two-level SR model. However our recent study [K. Nakajima et al., J. Phys. Soc. Jpn. 84, 054301 (2015)] using EUV free-electron laser excitation of helium atoms, where SR was observed at wavelengths of 502, 668, and 728 nm, revealed behaviour which necessitates a full multi-level treatment of the SR development. In this paper, we report simulations of the initial excitation by the FEL pulses, and the subsequent development of multi-level SR. The results of the simulation reproduce the experimental findings, and reveal that competitive SR on two transitions with a common upper level plays an important role in the development of the system.

DOI： 10.7566/JPSJ.85.034301

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We report extragalactic observations of two fluorine-bearing species, hydrogen fluoride (HF) and fluoronium (H2F+), in the z = 0.89 absorber in front of the lensed blazar PKS 1830-211 with the Atacama Large Millimeter/submillimeter Array. HF was detected toward both southwest and northeast images of the blazar, with column densities &gt; 3.4 x 10(14) cm(-2) and 0.18 x 10(14) cm(-2), respectively. H2F+ was not detected, down to an upper limit (3 sigma) of 8.8 x 10(11) cm(-2) and an abundance ratio of [H2F+]/[HF] &lt;= 1/386. We also searched for H2F+ toward the Galactic sources NGC 6334 I and W51C, and toward Galactic center clouds with the Herschel HIFI spectrometer.(6) The upper limit on the column density was derived to be 2.5 x 10(11) cm(-2) in NGC 6334 I, which is 1/68 of that for H2Cl+. In constrast, the ortho transition of H2Cl+ is detected toward PKS 1830-211. To understand the small abundance of interstellar H2F+, we carried out laboratory experiments to determine the rate constants for the ion-electron recombination reaction by infrared time-resolved spectroscopy. The constants determined are k(e)(209 K) = (1.1 +/- 0.3) x 10(-7) cm(3) s(-1) and (0.46 +/- 0.05) x 10(-7) cm(3) s(-1) for H2F+ and H2Cl+, respectively. The difference in the dissociative recombination rates between H2F+ and H2Cl+ by a factor similar to 2 and the cosmic abundance ratio [F]/[Cl] approximate to 1/6 are not enough to explain the much smaller abundance of H2F+. The difference in the formation mechanism of H2F+ and H2Cl+ in interstellar space would be a major factor in the small abundance of H2F+.

DOI： 10.3847/0004-637X/822/2/115

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

Using multilevel (161-level) numerical simulations beyond the rotating-wave approximation, we investigate the single-atom response of helium to intense pulses of radiation with properties characteristic of a self-amplified spontaneous emission (SASE) free-electron laser (FEL) source, and central wavelengths resonant with 1snp excitation (n = 3,4). The results show a complete breakdown of the two-level approximation and suggest that, under typical experimental conditions, levels other than the resonant level are significantly populated. We discuss the implications for the subsequent development of superfluorescence (a collective effect) from the excited atomic medium and compare the results to recent experiments.

DOI： 10.1103/PhysRevA.94.063416

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SPAN (SPectroscopy of Atomic Neutrino) project aims to determine the absolute neutrino mass. The process we plan to use is a cooperative de-excitation of atoms in a metastable level emitting a neutrino pair associated with a photon. The photon energy spectrum of this process contains information on the absolute mass of neutrino. Key items of this experiment are a rate amplification using macro-coherence in a target medium in case of plural particles emission and an external triggering of the emission in order to scan the spectrum. We have demonstrated the rate amplification in two-photon emission from para-hydrogen gas which was coherently excited to its first vibrationally excited state. The coherence in the medium was generated by irradiating two driving laser pulses. The emission was stimulated by irradiating a mid-infrared laser pulse. The enhancement factor of more than 10(18) with respect to the spontaneous emission was achieved. This paper briefly summarizes the results.

DOI： 10.1088/1742-6596/718/6/062043

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Other Link： http://orcid.org/0000-0002-0567-6881

Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.71.2.0_541

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Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.71.2.0_528

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DOI： 10.11316/jpsgaiyo.71.2.0_577

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DOI： 10.1088/0953-4075/48/15/159601

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Other Link： http://orcid.org/0000-0002-0567-6881

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We observed infrared absorption spectra of tetrahedral silicon tetrafluoride (SiF4) and its clusters in solid parahydrogen. The spectra were assigned by a temporal change of the peak intensity with annealing and previous studies in the gas and other matrices. It was found that the SiF4 monomer does not rotate in solid parahydrogen in spite of its small size and the absence of the permanent electric dipole moment. The dimer spectra are similar to those in the gas phase except for complicated sub-structures. Some other peaks were tentatively assigned to trimer and larger clusters. Clusters with other impurities were also observed. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cplett.2015.04.057

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

A cw-OPO laser system has been used to measure pressure broadening coefficients for the v(4) vibration-rotation transitions of CH3F by using Stark modulated Lamb dips. Eight pressure coefficients were determined from various pressure data, where each line shape was fitted to the Lorentzian function. The (r)Q(1,0) coefficient was found to be largely different from that of R-r(0,0), where the upper states of both transitions have the same J and K values but different parities of the l-type doublet. The coefficient for (r)Q(7,4) obtained in the present study agrees with that obtained by a Voigt profile analysis (Cartlidge and Butcher, 1990). (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cplett.2014.11.040

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We report the observation of superfluourescence at wavelengths (in air) of 501.6 nm, 667.8 nm, and 728.1 nm following the excitation of helium atoms with free-electron laser pulses at wavelengths of 53.7 nm (n = 3 excitation) and 52.2 nm (n = 4 excitation). The observed wavelengths of the superfluorescence pulses correspond to 1s3p-1s2s, 1s3d-1s2p, and 1s3s-1s2p transitions. Observation of superfluorescence on these transitions implies either competing cascade decays, or direct excitation of non-dipole allowed transitions. We have studied the time structure of the emitted pulses using a streak camera, and the results cannot be explained by straightforward considerations using the usual model for two-level superfluorescence.

DOI： 10.1088/0953-4075/48/10/105002

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

Through a spectral line survey observation with Nobeyama 45-m radio telescope in the 28-50 GHz region toward a late type star IRC+10216, a series of lines of a linear molecule was found in 1995. The rotational constant was determined to be 1376.8641(43) MHz, and the molecule is called B1377. After the detection, various studies related this species were carried out, which are presented in this paper, including Aoki's pioneering prediction and radio searches for NCO-, NCS-, and CCH-, etc. Finally, in 2006, McCarthy et al. succeeded in laboratory detection of the C6H- species by mm wave and FTMW spectroscopy and proved that the C6H- anion is B1377. We also report recent laboratory studies in the following topics :(1) time-resolved Fourier transform (FT) emission and absorption spectroscopy of molecular ions to obtain reaction rate constants, (2) FT infrared absorption spectrum of the H2F+ ion.

DOI： 10.1063/1.4906691

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

DOI： 10.1088/0953-4075/48/15/159601

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS INC  

We report on coherent enhancement of two-photon emission from the excited vibrational state of molecular hydrogen triggered by irradiating mid-infrared pulses externally. We previously observed the two-photon emission triggered by the internally generated fourth Stokes photons. By injecting independent mid-infrared pulses externally, it is possible to control the experimental parameters and investigate the mechanism in more detail. In this article, we describe the two-photon emission using the external trigger pulses. Its spectrum and dependence on the energy and timing of the trigger pulse are presented along with numerical simulations based on the Maxwell-Bloch equations. The measured number of emitted photons is 6 x 10(11) photons/pulse and the resulting enhancement factor from the spontaneous emission is more than 10(18). This value is three orders of magnitude higher than that of the previous experiment. External control of the emission process is expected to be essential for observation of the weaker process of radiative emission of a neutrino pair.

DOI： 10.1093/ptep/ptv103

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

We recently reported an experiment which focused on demonstrating the macro-coherent amplification mechanism. This mechanism, which was proposed for neutrino mass measurements, indicates that a multi-particle emission rate should be amplified by coherence in a suitable medium. Using a para-hydrogen molecule gas target and the adiabatic Raman excitation method, we observed that the two photon emission rate was amplified by a factor of more than 10(15) from the spontaneous emission rate. This paper briefly summarizes the previous experimental result and presents the current status and the future prospect.

DOI： 10.1007/s10751-015-1177-1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

In this paper, we report the results of measurements of the intensities and delays of super-radiance decays from excited helium atoms at multiple wavelengths. The experiment was performed using extreme ultraviolet radiation produced by the free electron laser at the SPring-8 Compact SASE Source test accelerator facility as an excitation source. We observed super-radiant transitions on the 1s3p -&gt; 1s2s (lambda = 502 nm), 1s3d -&gt; 1s2p (lambda = 668 nm), and 1s3s -&gt; 1s2p (lambda = 728 nm) transitions. The pulse energy of each transition and its delay time were measured as a function of the target helium gas density. Several interesting features of the data, some of which appear to contradict with the predictions of the simple two-level super-radiance theory, are pointed out.

DOI： 10.7566/JPSJ.84.054301

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Laser-induced near-infrared (NIR) emission spectra of neutral bismuth timer, Bi-3, embedded in solid neon matrixes at 3 K were recorded in a range 870-1670 nm. Using photoexcitation with low energy photons at 1064 nm, two emission band systems were newly identified by their origin bands at T-0 = 6600 and 8470 cm(-1). Accordingly, spectral assignment for three NIR emission band systems reported recently was partly revised for the one with its origin band at T-0 = 7755 cm(-1) and reconfirmed for the others at T-0 = 9625 and 11 395 cm(-1). Energy splitting by spin-orbit coupling between the pair of electronic energy levels in the ground state of bismuth trimer, Bi-3, both having a totally symmetric vibrational mode of frequency at omega"(e) = 150 cm(-1), was determined to be 1870 +/- 1.5 cm(-1). Transitions from the pair of electronically excited states, locating at T-0 = 8470 and 9625 cm(-1) above the ground state and separated by spin-orbit coupling of 1155 cm(-1), have relatively long decay constants of tau similar to 0.2 and similar to 0.1 ms, respectively.

DOI： 10.1021/jp509714f

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.70.1.0_771

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DOI： 10.11316/jpsgaiyo.70.1.0_86

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DOI： 10.11316/jpsgaiyo.70.1.0_772

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DOI： 10.11316/jpsgaiyo.70.1.0_668

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS INC  

In this paper, we describe an experiment which was conducted to explore the macro-coherent amplification mechanism using a two-photon emission process from the first vibrationally excited state of the para-hydrogen molecule. Large coherence in the initial state was prepared by the adiabatic Raman method, and the lowest Stokes sideband was used as a trigger field. We observed coherent two-photon emission consistent with the expectation of the Maxwell-Bloch equation derived for the process, whose rate is larger by many orders of magnitude than that of spontaneous emission.

DOI： 10.1093/ptep/ptu152

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

We describe in this paper a fast and efficient method of producing a high density of barium (Ba) atoms in the D-1(2) metastable state, which is a candidate initial state for a new class of cooperative and coherent optical process called paired superradiance (PSR). In the experiment, Ba atoms are excited first by laser light to the P-1(1) state and then brought to the desired state D-1(2) via radiative transition in the superradiance (SR) mode. It is found that a production efficiency (from S-1(0) to D-1(2)) of more than similar to 30% is achieved within a time interval of a few nanoseconds for a Ba density n > 10(19) m(-3). Several key features of SR important for future PSR experiments are also studied.

DOI： 10.7566/JPSJ.83.044301

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS INC  

It has recently been argued that atoms and molecules may become good targets for determining neutrino parameters still undetermined, if the atomic/molecular process is enhanced by a new kind of coherence. We compute the photon energy spectrum rate arising from coherent radiative neutrino pair emission processes of metastable excited states of I-2 and its isovalent molecules, vertical bar Av &gt; -&gt; vertical bar Xv'&gt; + gamma +nu(i)nu(j) and vertical bar A' v &gt; -&gt; vertical bar Xv '&gt; + gamma + nu(i)nu(j), with gamma an IR photon and nu(i(j)) the i (j)th neutrino mass eigenstates, and show how fundamental neutrino parameters may be determined. Energies of electronically excited states of I-2, including the effect of spin-orbit couplings, were calculated by the multiconfigurational second-order perturbation (CASPT2) method. Summation over many vibrational levels of intermediate states is fully incorporated. Unlike atomic candidates with a much larger energy difference, such as Xe, I-2 transitions from a vibrational level A(v = 0) to X(v' = 24) give us an opportunity to determine the mass type (Majorana vs Dirac distinction) and theMajorana CPV (charge-conjugation parity violating) phases, although the rate is much smaller.

DOI： 10.1093/ptep/ptt118

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：COPERNICUS GESELLSCHAFT MBH  

Column-averaged dry-air mole fractions of methane (XCH4), retrieved from Greenhouse gases Observing SATellite (GOSAT) short-wavelength infrared (SWIR) spectra, were validated by using aircraft measurement data from the National Oceanic and Atmospheric Administration (NOAA), the US Department of Energy (DOE), the National Institute for Environmental Studies (NIES), the HIAPER Pole-to-Pole Observations (HIPPO) program, and the GOSAT validation aircraft observation campaign over Japan. In the calculation of XCH4 from aircraft measurements (aircraft-based XCH4), other satellite data were used for the CH4 profiles above the tropopause. We proposed a data-screening scheme for aircraft-based XCH4 for reliable validation of GOSAT XCH4. Further, we examined the impact of GOSAT SWIR column averaging kernels (CAK) on the aircraft-based XCH4 calculation and found that the difference between aircraft-based XCH4 with and without the application of the GOSAT CAK was less than +/- 9 ppb at maximum, with an average difference of -0.5 ppb. We compared GOSAT XCH4 Ver. 02.00 data retrieved within +/- 2 degrees or +/- 5 degrees latitude-longitude boxes centered at each aircraft measurement site with aircraft-based XCH4 measured on a GOSAT overpass day. In general, GOSAT XCH4 was in good agreement with aircraft-based XCH4. However, over land, the GOSAT data showed a positive bias of 1.5 ppb (2.0 ppb) with a standard deviation of 14.9 ppb (16.0 ppb) within the +/- 2 degrees (+/- 5 degrees) boxes, and over ocean, the average bias was 4.1 ppb (6.5 ppb) with a standard deviation of 9.4 ppb (8.8 ppb) within the +/- 2 degrees (+/- 5 degrees) boxes. In addition, we obtained similar results when we used an aircraft-based XCH4 time series obtained by curve fitting with temporal interpolation for comparison with GOSAT data.

DOI： 10.5194/amt-7-2987-2014

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Laser induced fluorescence (LIF) spectroscopy was applied to small bismuth clusters embedded in a solid neon matrix at 3 K. Near infrared (NIR) optical emission spectra were recorded in a range of 6200-11 600 cm(-1) by an excitation with 1.79 eV photons using a pulsed dye laser system. Three new NIR band systems were identified by their origin bands at 8207, 9625 and 11 395 cm(-1). Each of the NIR systems exhibited the vibrational progression with a common lower state frequency at 151 cm(-1). Temporal decay profiles for selected NIR emission bands showed upper state lifetimes on the order of a hundred of microseconds, explainable by the transition between mixed spin states. Low-lying electronic states for small bismuth clusters, Bi-n (n = 2-4), are discussed along the theory and experiment reported so far.

DOI： 10.1140/epjd/e2012-30529-x

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

We present high-resolution infrared absorption spectra of chloromethyl radical produced by in situ UV photolysis of chloroiodomethane isolated in solid parahydrogen. The radicals were stable over a few days in solid parahydrogen kept at 3.6 K. Analysis of the rotation-vibration spectra revealed that the radical exhibited quantized one-dimensional rotational motion about the C-Cl bond, while the ortho and para nuclear spin species were still clearly distinguishable in the spectra. Temporal change of the spectra indicated that the nuclear spin conversion between the ortho and para nuclear spin species of the radical in solid parahydrogen occurred in a time scale of a few hours at 3.6 K. It was also. found that the nuclear spin conversion became significantly slower in a higher concentration of chloroiodomethane.

DOI： 10.1021/jp312122p

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：COPERNICUS GESELLSCHAFT MBH  

Atmospheric column-averaged mole fractions of carbon dioxide (XCO2) at 53 locations around the world were derived from aircraft measurements covering the altitude range of about 1-10 km. We used CO2 vertical profile measurements from three major carbon cycle programs, a global climatological data set of air number density profiles and tropopause height for calculating XCO2 for the period of 2007-2009. Vertical profiles of the CO2 mixing ratio are complemented by tall tower data up to 400 m from the earth's surface and by simulated profiles in the stratosphere from a chemistry-transport model. The amplitude of the seasonal cycle of calculated XCO2 values shows clear latitudinal dependence, and the amplitude decreases from about 10 ppm at high latitudes in the Northern Hemisphere to at most 2 ppm in the tropics and the Southern Hemisphere. The uncertainties of XCO2 were estimated from assumptions about CO2 profiles for each flight. Typically, uncertainties were less than 1 ppm; thus, this data set is within the level of uncertainty needed for primary validation of XCO2 measurements by the Greenhouse gases Observing SATellite (GOSAT) and by future satellite missions for monitoring greenhouse gases.

DOI： 10.5194/acp-13-5265-2013

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Language：English   Publishing type：Research paper (scientific journal)  

Difference-frequency generation of 4.8 μm mid-infrared light was performed using a waveguide periodically poled LiNbO3 (PPLN) crystal. 871 and 1064 nm external-cavity diode lasers followed by tapered amplifiers were used as pump sources. A conversion efficiency of ̃2%/W with the output power of 2 mW was achieved even under considerable absorption of the crystal at this wavelength. Lamb-dip spectroscopy of carbonyl sulfide was demonstrated showing the satisfactory performance of this device for saturation spectroscopy. The observed dip width shows that the laser linewidth is ̃2 MHz, which corresponds to those of the pump lasers. © 2013 Optical Society of America.

DOI： 10.1364/OL.38.002825

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：COPERNICUS GESELLSCHAFT MBH  

Column-averaged dry air mole fractions of carbon dioxide (XCO2) retrieved from Greenhouse gases Observing SATellite (GOSAT) Short-Wavelength InfraRed (SWIR) observations were validated with aircraft measurements by the Comprehensive Observation Network for TRace gases by AIrLiner (CONTRAIL) project, the National Oceanic and Atmospheric Administration (NOAA), the US Department of Energy (DOE), the National Institute for Environmental Studies (NIES), the HIAPER Pole-to-Pole Observations (HIPPO) program, and the GOSAT validation aircraft observation campaign over Japan. To calculate XCO2 based on aircraft measurements (aircraft-based XCO2), tower measurements and model outputs were used for additional information near the surface and above the tropopause, respectively. Before validation, we investigated the impacts of GOSAT SWIR column averaging kernels (CAKs) and the shape of a priori profiles on the aircraft-based XCO2 calculation. The differences between aircraft-based XCO2 with and without the application of GOSAT CAK were evaluated to be less than +/-0.4 ppm at most, and less than +/-0.1 ppm on average. Therefore, we concluded that the GOSAT CAK produces only a minor effect on the aircraft-based XCO2 calculation in terms of the overall uncertainty of GOSAT XCO2. We compared GOSAT data retrieved within +/-2 or +/-5 degrees latitude/longitude boxes centered at each aircraft measurement site to aircraft-based data measured on a GOSAT overpass day. The results indicated that GOSAT XCO2 over land regions agreed with aircraft-based XCO2, except that the former is biased by -0.68 ppm (-0.99 ppm) with a standard deviation of 2.56 ppm (2.51 ppm), whereas the averages of the differences between the GOSAT XCO2 over ocean and the aircraft-based XCO2 were -1.82 ppm (-2.27 ppm) with a standard deviation of 1.04 ppm (1.79 ppm) for +/-2 degrees (+/-5 degrees) boxes.

DOI： 10.5194/acp-13-9771-2013

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

We studied diffusion of hydrogen fluoride (HF) in solid parahydrogen (pH(2)) around 4 K. Diffusion rates were determined from time dependence of FT-IR spectra of HF monomers. The absorption of HF monomers shows temporal decay due to dimerization reaction via diffusion. It was found that the rates are affected by the sample temperature, the initial HF concentration, and annealing of samples. The observed non-Arrhenius-type temperature dependence suggests that the diffusion is dominated by a quantum tunneling process, that is, "quantum diffusion." Deceleration of the diffusion in condensed samples and acceleration in annealed samples were also observed. These results can be attributed to the fact that lower periodicity of samples due to impurities or defects suppresses the quantum tunneling. It seems to be difficult to explain the observed dependences by three possible diffusion mechanisms, exchange of chemical bonds, direct cyclic exchange, and exchange with mobile vacancy. Therefore, we propose a hypothetical mechanism by exchange of vacancies originating from quantum effect. (C) 2013 AIP Publishing LLC.

DOI： 10.1063/1.4808035

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

The coherence decay of the v = 2 vibrational state (vibrons) of solid parahydrogen was measured via time-resolved coherent anti-Stokes Raman spectroscopy. We found that the decay curve has a non-exponential time profile in the time scale of 200 ns at a low temperature below 5 K and a low orthohydrogen impurity concentration (similar to 0.01%). This behavior, as also observed in the case of the v = 1 vibrons, represents a signature of band structure of the v = 2 state in the solid phase. The maximum coherence decay time of 50 ns in an exponential part was achieved, which shows excellence of the v = 2 state for coherent processes. We also found that finite temperatures, orthohydrogen impurities, and other structural inhomogeneity accelerate the decay, hiding the non-exponential feature of the vibron band. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4773893]

DOI： 10.1063/1.4773893

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DOI： 10.5194/acp-13-9213-2013

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Infrared absorption spectra of methyl fluoride with ortho-hydrogen (ortho-H-2) clusters in a solid para-hydrogen (para-H-2) crystal at 3.6 K were studied in the C-H stretching fundamental region (similar to 3000 cm(-1)) using an FTIR spectrometer. As shown previously, the nu(3) C-F stretching fundamental band of CH3F-(ortho-H-2)(n) (n = 0, 1, 2,...) clusters at 1040 cm(-1) shows a series of n discrete absorption lines, which correspond to different-sized clusters. We observed three unresolved broad peaks in the C-H stretching region and applied this cluster model to them assuming the same intensity distribution function as the nu(3) band. A fitting analysis successfully gave us the linewidth and lineshift of the components in each vibrational band. It was found that the separately determined linewidth, matrix shift of the band origin, and cluster shift are dependent on the vibrational mode. From the transition intensities of the monomer component derived from the fitting analysis, we discuss the mixing ratio of the vibrational modes due to Fermi resonance. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4765698]

DOI： 10.1063/1.4765698

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：COPERNICUS GESELLSCHAFT MBH  

Aircraft measurements of carbon dioxide and methane over Tsukuba (36.05 degrees N, 140.12 degrees E) (February 2010) and Moshiri (44.36 degrees N, 142.26 degrees E) (August 2009) were made to calibrate ground-based high-resolution Fourier Transform Spectrometers (g-b FTSs) and to compare with the Greenhouse gases Observing SATellite (GOSAT). The aircraft measurements over Tsukuba in February 2010 were successful in synchronizing with both the g-b FTS and GOSAT for the first time. Airborne in situ and flask-sampling instruments were mounted on the aircraft, and measurements were carried out between altitudes of 0.5 and 7 km to obtain vertical profiles of carbon dioxide (CO2), methane (CH4), and other gaseous species.
By comparing the g-b FTS measurements with the airborne measurements, the column-averaged dry air mole fractions of CO2 (X-CO2) and CH4 (X-CH4) retrieved from the g-b FTS measurements at Tsukuba were biased low by 0.33 +/- 0.11% for X-CO2 and 0.69 +/- 0.29% for X-CH4.
The g-b FTS values at Moshiri were biased low by 1.24% for X-CO2 and 2.11% for X-CH4. The GOSAT data show biases that are 3.1% +/- 1.7% lower for X-CO2 and 2.5% +/- 0.8% lower for X-CH4 than the aircraft measurements obtained over Tsukuba.

DOI： 10.5194/amt-5-2003-2012

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS INC  

We systematically investigate the new experimental method of using atoms or molecules to measure the important parameters of neutrinos that are still to be determined: the absolute mass scale, the mass hierarchy pattern (normal or inverted), the neutrino mass type (Majorana or Dirac), and the CP-violating phases, including Majorana phases. Most of these observables are difficult to measure in neutrino oscillation experiments. There are advantages to using atomic targets, such as the closeness of available atomic energies to anticipated neutrino masses, over nuclear target experiments such as the end point spectrum of beta decay and two-electron line spectrum in the neutrinoless double beta decay, both of which address some of the overlapping objectives with atomic/molecular experiments. A disadvantage of using atomic targets, the smallness of rates, is overcome by the macro-coherent amplification mechanism. The atomic or molecular process we use is a cooperative deexcitation of a collective body of atoms in a metastable level vertical bar e > emitting a neutrino pair and a photon: vertical bar e > -> vertical bar g > + gamma + nu(i)nu(j), where nu(i)s are neutrino mass eigenstates. The macro-coherence is developed by trigger-laser irradiation of two colors, which frequently causes the two-photon process vertical bar e > <-> vertical bar g > + gamma + gamma, vertical bar e > + gamma <-> vertical bar g > + gamma inside the target. We discuss important aspects of the macro-coherence development in detail, by setting up the master equation for the target Bloch vector (whose components are population difference and medium polarization) and the propagating electric field. Our master equation includes the effects of phase decoherence of medium polarization and decay of population difference. The spectral rate (the number of events per unit time) of macro-coherent radiative emission of a neutrino pair has three parts, and is given by a factorized formula of the form (overall omega-independent rate denoted by Gamma(0)) x (spectral shape function denoted by I (omega)) x (time-evolving dynamical factor), where omega is the photon energy. The constant factor Gamma(0) determines the overall rate in the unit of 1/time, and for Xe it is of the order of 1Hz(n/10(22) cm(-3))(3) (V/10(2) cm(3)). The dynamical factor is time dependent and is given by the space integrated quantity, over the entire target, of the product of the magnitude squared of the coherent polarization and the field strength (in the units of the maximally extractable energy density) stored inside the target. The asymptotic value of the time-evolving dynamical factor is given by the contribution of the field condensate accompanied by macroscopic coherence, which is calculated using the static limit of the master equation. With an appropriate choice of heavy target atoms or molecules such as Xe and I-2 that have a large M1 x E1 matrix element between vertical bar e > and vertical bar g >, we show that one can determine three neutrino masses along with distinction of the mass hierarchy pattern (normal or inverted) by measuring the spectral shape I (omega).If one uses a target of available energy of a fraction of 1 eV, the most experimentally challenging observable, the Majorana CP phases may be determined, comparing the detected rate with differences of theoretical expectations which exist at the level of several percent. The Majorana CP-violating phase is expected to be crucial to the understanding of the matter-antimatter imbalance in our universe. Our master equation, when applied to E1 x E1 transitions such as pH(2) vibrational Xv = 1 -> 0, can describe explosive paired superradiance events in which most of the energy stored in vertical bar e > is released in the order of a few nanoseconds. The present paper is intended to be self-contained, explaining some details of related theoretical works in the past, and reports on new simulations and the ongoing experimental efforts of the project to realize neutrino mass spectroscopy using atoms/molecules.

DOI： 10.1093/ptep/pts066

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

Solid para-H-2 is a promising gain medium for stimulated Raman scattering, due to its high number density and narrow Raman linewidth. In preparation for the design of a cw solid hydrogen Raman laser, we have made the first measurements, to our knowledge, of the index of refraction of a solid para-H-2 crystal, in the wavelength range of 430-1100 nm. For a crystal stabilized at 4.4 K, this refractive index is measured to be n(p-H2) 1.130 +/- 0.001 at 514 nm. A slight, but significant, dependence on the final crystal-growth temperature is observed, with higher n(p-H2) at higher crystal-growth temperatures. Once a crystal is grown, it can be heated up to 10 K with no change in n(p-H2). The refractive index varies only slightly over the observed wavelength range, and no significant birefringence was observed. (C) 2011 Optical Society of America

DOI： 10.1364/OL.36.000840

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

We report measurements of FT-IR absorption spectroscopy of HF, DF, and their clusters in solid parahydrogen (pH(2)). The observed spectra contain many absorption lines which were assigned to HF monomers, HF polymers, and clusters with other species, such as N-2, O-2, orthohydrogen (oH(2)), etc. The rotational constants of HF and DF monomers were determined from the cooperative transitions of the vibration of solid pH(2) and the rotation of HF and DF. Small reduction of the rotational constants indicates that HF and DF are nearly free rotors in solid pH(2). Time dependence of the spectra suggests that HF and DF monomers migrate in solid pH(2) and form larger polymers, probably via tunneling reactions through high energy barriers on inserting another monomer to the polymers. The line width of HF monomers in solid pH(2) was found to be 4 cm(-1), which is larger than that of other hydrogen halides in solid pH(2). This broad line width is explained by rapid rotational relaxation due to the accidental coincidence between the rotational energy of HF and the phonon energy with maximum density of states of solid pH(2) and the rotational translational coupling in a trapping site.

DOI： 10.1021/jp207419m

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

Continuous validation of data observed by satellites, such as Greenhouse gases Observing SATellite (GOSAT), is important to qualify the long-term trends of greenhouse gases. High-precision data over the restricted region measured by ground-based high-resolution Fourier transform spectrometers (g-b FTS), airborne in-situ instruments, and flask sampling devices have been used for the validation of satellite data. As part of CAL/VAL (Calibration/Validation) activities of the GOSAT, airborne flight campaigns were performed over Tsukuba and Moshiri using the ground-based FTS, airborne in-situ and flask devices, and 1.57-mu m Laser Absorption Sensor (LAS). Airborne flask sampling and insitu carbon dioxide (CO2) sensors were carried out to obtain vertical profiles of the CO2 mixing ratio while ground-based FTS and LAS measured solar direct spectra and weighted column-averaged CO2, respectively. Those results were used to decide a calibration factor of the ground-based FTS and compared with GOSAT products over Tsukuba. We will report the comparison results of the aircraft campaign measurements and the retrieval value from the FTS.

DOI： 10.1117/12.898549

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Other Link： http://orcid.org/0000-0002-0567-6881

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

The production of enriched para-H-2 is useful for many scientific applications, but the technology for producing and measuring para-H-2 is not yet widespread. In this note and in the accompanying auxiliary material, we describe the design, construction, and use of a versatile standalone converter that is capable of producing para-H-2 enrichments of up to &gt;= 99.99% at continuous flow rates of up to 0.4 SLM. We also discuss para-H-2 storage and back conversion rates, and improvements to three techniques (thermal conductance, NMR, and solid hydrogen impurity spectroscopy) used to quantify the para-H-2 enrichment.

DOI： 10.1063/1.3072881

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

The nuclear spin conversion of CH(4) and CD(4) isolated in solid parahydrogen was investigated by high resolution Fourier transform infrared spectroscopy. From the analysis of the temporal changes of rovibrational absorption spectra, the nuclear spin conversion rates associated with the rotational relaxation from the J=1 state to the J=0 state for both species were determined at temperatures between 1 and 6 K. The conversion rate of CD(4) was found to be 2-100 times faster than that of CH(4) in this temperature range. The faster conversion in CD(4) is attributed to the quadrupole interaction of D atoms in CD(4), while the conversion in CH(4) takes place mainly through the nuclear spin-nuclear spin interaction. The conversion rates depend on crystal temperature strongly above 3.5 K for CH(4) and above 2 K for CD(4), while the rates were almost constant below these temperatures. The temperature dependence indicates that the one-phonon process is dominant at low temperatures, while two-phonon processes become important at higher temperatures as a cause of the nuclear spin conversion. (c) 2008 American Institute of Physics.

DOI： 10.1063/1.2889002

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Photochemical reactions of molecules in solid orthodeuterium (o-D-2) have been studied by high-resolution infrared spectroscopy and compared with previous results obtained in solid parahydrogen (p-H-2). Ultraviolet photoplysis of CD3I molecules in solid o-D2 yielded CD3 radicals and iodine atoms efficiently, which indicates a small cage effect in solid o-D2, as in the case of solid p-H2. The Fourier transform infrared spectrum of the nu(3) vibrational band of CD3 showed a rotational structure with additional splitting due to crystal field interactions. The magnetic dipole transition (2P(1/2) (&lt;-) P-2(3/2)) of the I atom isolated in solid o-D-2 was observed together with a strong rotational satellite of deuterium molecules through the electron-roton coupling in solid hydrogen. The tunneling reaction between CD3 and D-2 was not observed in a time scale of a few days, which gives the upper limit of the tunneling,reaction rate of 10(-8) s(-1) at 4.2 K.

DOI： 10.1021/jp0761113

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The ortho-to-para nuclear spin ratio of cyclopropenylidene ( cyclic C3H2) in TMC-1 cores was investigated using the 45 m radio telescope at Nobeyama Radio Observatory. We have observed four ortho lines (J(KaKc) = 2(12) - 1(01), 3(12) - 3(03), 3(21) - 3(12), and 3(30) - 3(21)) and four para lines (J(KaKc) 2(02) - 1(11), 2(11) - 2(02), 2(20) - 2(11), and 3(22) - 3(13)) of cyclic C3H2 in six cores in TMC-1. A statistical equilibrium analysis of the observed intensities revealed apparent correlation between the ortho-to-para ratio of cyclic C3H2 and chemical evolution of the molecular cloud; the ortho-to-para ratio in younger cores is less than 2, while that in older cores is close to the statistical ratio of 3. A simple chemical model calculation indicates that the correlation is ascribed to the conservation of nuclear spin angular momenta in chemical reactions relevant to the production, destruction, and reproduction of cyclic C3H2. Since cyclic C3H2 has been observed in a variety of sources, the ortho-to-para ratio of cyclic C3H2 may be a useful probe of chemical evolution of molecular clouds.

DOI： 10.1086/501041

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

Despite several suggestions concerning the existence of negatively charged molecules and negative atomic ions in molecular clouds, few attempts have been made to search for negative ions in molecular clouds. In the present study, we extensively searched for three negative molecular ions (CCH-, NCO-, and NCS-) in a dark cloud, L134N, using the Nobeyama 45-m radio telescope. The three negative ions are molecules whose rotational constants have been reported based on laboratory experiments. After a long accumulation, a trace amount of an unidentified emission line was detected at a frequency close to the theoretical prediction of the J = 1-0 transition of CCH-. If this unidentified line is attributable to CCH-, the observed emission intensity would provide an estimation of the column density of CCH- in L134N to be 1.0 x 10(11) cm(-2), which corresponds to a fractional abundance of 5 x 10(-12) relative to hydrogen. However, our recent observation using the IRAM 30-m telescope did not reproduce the J = 1-0 signal, nor detect any trace of the J = 2-1 transition. Thus, the identification of CCH- in L134N is not yet confirmed. As for other ions, signals of neither NCO- nor NCS- were detected in L134N. Although we also searched for the three negative ions in a translucent cloud, CB228, and a star-forming region, SgrB2, no signals were detected. The upper limit abundances of the ions in these clouds are discussed limit abundances of the ions in these clouds are discussed.

DOI： 10.1093/pasj/57.2.325

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

We report the preliminary results of our experiments with stimulated Raman scattering in para-hydrogen crystal aimed at developing a continuously tunable laboratory laser source of mid-infrared radiation. With laser pulses at 532 nm, a conversion efficiency for the first Stokes beam of as much as 20% in the forward direction was observed through a single-pass, 5-cm-long crystal. Generation of mid-infrared pulses at 4.5 mum was achieved by use of the output of a near-infrared pulsed laser (1.6 mum, 3 ns), and an absorption spectrum of gaseous CD4 molecules was successfully recorded. These results suggest use of the solid para-hydrogen Raman shifter as a promising light source for mid-infrared spectroscopy. (C) 2003 Optical Society of America.

DOI： 10.1364/OL.28.000037

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

We report the results of our preliminary investigations into the suitability of condensed-phase parahydrogen as a Raman-shifting medium for infrared cavity ringdown laser absorption spectroscopy. We have observed the conversion of similar to10-ns pulses of 532-nm radiation into first-, second-, and third-order vibrational Stokes radiation in bulk liquid and solid parahydrogen after a single 11-cm pass. Unexpectedly, we find that liquid H-2 yields more efficient conversion than solid H-2 with certain focal geometries, and that in the case of the solid, a collimated or loosely focused pump geometry is more efficient than a tight focus. (C) 2003 American Institute of Physics.

DOI： 10.1063/1.1556560

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Language：Japanese   Publisher：The Physical Society of Japan  

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DOI： 10.11316/jpsgaiyo.71.2.0_181

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Authorship：Lead author,　Corresponding author   Publisher：The Spectroscopical Society of Japan  

DOI： 10.5111/bunkou.63.2_71

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researchmap

researchmap

researchmap

researchmap

researchmap