Nuclear spin conversion of hydrogen and methane molecules inside low-temperature condensed layers

Yamakawa, Koichiro

Bunko Kenkyu, 72(5), p.187 - 198, 2023/10

Molecules including hydrogen nuclei in the rotationally symmetric positions are classified into the nuclear spin isomers, according to their resultant spin. Owing to the symmetry restriction originating from the indistinguishability of the identical particles, each isomer occupies only specific rotational levels. The conversion between the isomers is promoted in condensed systems, where the excess rotational energy of a converting molecule is dissipated. In this review, I focus on the fundamental molecules of hydrogen and methane, and expound studies on their nuclear spin conversion inside condensed layers at low temperatures.

An Isotope-labeling study of CO formation pathways in molecular clouds; Ultraviolet photolysis of CO-HO ice

Hirayama, Akemi*; Arakawa, Ichiro*; Yamakawa, Koichiro

Astrophysical Journal, 951(2), p.132_1 - 132_12, 2023/07

https://doi.org/10.3847/1538-4357/acd547

With use of reflection-absorption infrared spectroscopy, we investigated the binary ice of CO and HO at 10 K under ultraviolet irradiation as an analogue of interstellar ice mantle. We employed HO instead of HO to distinguish the formation pathways of CO, and prepared mixed-ice samples under CO- and HO-rich conditions as well as bilayered one, where CO was condensed on HO ice. After the ultraviolet irradiation onto any sample, we detected infrared absorption bands of CO and COO, which were generated through the CO-CO and CO-HO reactions, respectively. We analyzed the irradiation-time dependence of the CO and COO column densities in CO-rich ice to determine the effective cross sections of the CO formation through the CO-CO and CO-HO reactions simultaneously.

Fast nuclear-spin conversion of H trapped and polarized in a CO matrix

Yamakawa, Koichiro; Ishibashi, Atsuki*; Namiyoshi, Toshinobu*; Azuma, Yuichi*; Arakawa, Ichiro*

Physical Review B, 102(4), p.041401_1 - 041401_5, 2020/07

https://doi.org/10.1103/PhysRevB.102.041401

Terahertz and mid-infrared spectroscopy of matrix-isolated clusters and matrix-sublimation ice of DO

Yamakawa, Koichiro; Nasu, Hirokazu*; Suzuki, Natsumi*; Shimizu, Genki*; Arakawa, Ichiro*

Journal of Chemical Physics, 152(17), p.174310_1 - 174310_13, 2020/05

https://doi.org/10.1063/5.0005766

We have established an apparatus for terahertz and mid-infrared spectroscopy in an ultrahigh vacuum and have measured absorption spectra of DO clusters trapped in solid Ar. To assign terahertz absorption peaks due to the DO dimer, trimer, and tetramer, the dependence of the spectrum on the annealing temperature and DO dilution was analyzed. The assignment was also examined by ab initio calculations with use of the ONIOM method, where flexibility of surrounding Ar atoms was systematically incorporated. We identified all of the intermolecular fundamentals of the dimer and those with significant intensities of the trimer and tetramer, whose structural symmetries were revealed to be broken down. After isolating the DO clusters in solid Ar, we sublimated only Ar atoms to leave behind matrix-sublimation ice, which was found to be amorphous- or crystal-like depending on the formation conditions: the dilution and sublimation-temperature. Since the crystallinity got higher with raising the dilution and sublimation-temperature, the diffusion of the DO monomer on the surface of sublimating solid Ar was found to be crucial to the crystallization of the sublimation ice.

Spectroscopic determination of interconversion rates among three nuclear spin isomers of methane in crystalline II

Sugimoto, Takeru*; Nasu, Hirokazu*; Arakawa, Ichiro*; Yamakawa, Koichiro

Journal of Chemical Physics, 150(18), p.184302_1 - 184302_5, 2019/05

https://doi.org/10.1063/1.5091070

We measured infrared absorption spectra of crystalline II of methane and succeeded in detecting a prominent Q(2) peak by rapid cooling after annealing as well as previously reported rovibrational and librational-vibrational peaks. The integral intensities of the R(0), R(1), and Q(2) peaks were found to show biexponential dependence on time. This clearly demonstrates the interconversion among the three nuclear-spin isomers occupying low-lying rotational levels.

Experimental study for the production cross sections of positron emitters induced from C and O nuclei by low-energy proton beams

Akagi, Takashi*; Yagi, Masashi*; Yamashita, Tomohiro*; Murakami, Masao*; Yamakawa, Yoshiyuki*; Kitamura, Keiji*; Ogura, Koichi; Kondo, Kiminori; Kawanishi, Shunichi*

Radiation Measurements, 59, p.262 - 269, 2013/12

https://doi.org/10.1016/j.radmeas.2013.07.005

In proton therapy, positron emitters are induced from C andO nuclei by protons on the beam path in the patient. Many studies for monitoring positron emitters with beam-induced PET technique have been performed by various groups to verify the proton beam range and the dose in the patient for quality assurance. The aim of this study was to develop a method for measuring the production cross sections of positron emitters using standard equipment for proton therapy. The time-activity curve was then obtained with a high-sensitivity PET scanner to extract the number of positron emitters produced in the target. The production cross sections for four reaction channels: O(p,pn)O, O(p,3p3n)C, O(p,2p2n)N, and C(p,pn)C were then measured. The cross sections for the O(p,pn)O reaction channel were consistent with data of previous experiments within the uncertainties, while those of C(p,pn)C were generally lower than data of previous experiments.

Full-coherent HHG-seeded EUV-FEL locked by EOS timing feedback

Ogawa, Kanade*; Sato, Takahiro*; Matsubara, Shinichi*; Okayasu, Yuichi*; Togashi, Tadashi*; Watanabe, Takahiro*; Takahashi, Eiji*; Midorikawa, Katsumi*; Aoyama, Makoto; Yamakawa, Koichi; et al.

Proceedings of 10th Conference on Lasers and Electro-Optics Pacific Rim and 18th OptoElectronics and Communications Conference and Photonics in Switching 2013 (CLEO-PR & OECC/PS 2013) (USB Flash Drive), 2 Pages, 2013/06

https://doi.org/10.1109/CLEOPR.2013.6600178

no abstracts in English

Photoionization of atoms and molecules by intense EUV-FEL pulses and FEL seeded by high-order harmonic of ultrashort laser pulses

Iwasaki, Atsushi*; Sato, Takahiro*; Owada, Shigeki*; Togashi, Tadashi*; Takahashi, Eiji*; Midorikawa, Katsumi*; Aoyama, Makoto; Yamakawa, Koichi; Kannari, Fumihiko*; Yagishita, Akira*; et al.

Reza Kenkyu, 40(9), p.687 - 690, 2012/09

http://joi.jlc.jst.go.jp/JST.Journalarchive/lsj1973/11.687

no abstracts in English

Extreme ultraviolet free electron laser seeded by high-order harmonic

Togashi, Tadashi*; Takahashi, Eiji*; Midorikawa, Katsumi*; Aoyama, Makoto; Yamakawa, Koichi; Sato, Takahiro*; Iwasaki, Atsushi*; Owada, Shigeki*; Yamanouchi, Kaoru*; Hara, Toru*; et al.

Proceedings of 11th International School and Symposium on Synchrotron Radiation in Natural Science (ISSRNS 2012), p.1 - 21, 2012/05

The 13th harmonic of a Ti:sapphire laser has been significantly amplified with the SCSS test accelerator. The temporal and spatial overlap of the electron beam and the high harmonic radiation were precisely tuned for achieving the seeded free electron laser operation. With numerical simulation the present HH-seeded FEL scheme could readily be applied to the wavelength region down to 10 nm.

Determination of the absolute two-photon ionization cross section of He by an XUV free electron laser

Sato, Takahiro*; Iwasaki, Atsushi*; Ishibashi, Kazuki*; Okino, Tomoya*; Yamanouchi, Kaoru*; Adachi, Junichi*; Yagishita, Akira*; Yazawa, Hiroki*; Kannari, Fumihiko*; Aoyama, Makoto; et al.

Journal of Physics B; Atomic, Molecular and Optical Physics, 44(16), p.161001_1 - 161001_5, 2011/08

https://doi.org/10.1088/0953-4075/44/16/161001

The resonant and non-resonant two-photon single ionization processes of He were investigated using intense free electron laser light in the extreme ultraviolet (XUV) region (53.4-61.4 nm) covering the 1s-2p and 1s-3p resonant transitions of He. On the basis of the dependences of the yield of He on the XUV light-field intensity at 53.4, 58.4, 56.0 and 61.4 nm, the absolute values of the two-photon ionization cross sections of He at the four different wavelengths and their dependence on the light-field intensity were determined for the first time.