研究者詳細 - 熊谷　純

論文 - 熊谷　純

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Decay dynamics of H atoms in solid hydrogen at 4.2 and 2.2 K. Controlling factor of tunneling reaction H + para-H2 査読有り

T. Miyazaki, S. Mori, T. Nagasaka, J. KUmagai, Y. Aratono, T. Kumada

J. Phys. Chem. A. 104 巻 ( 42 ) 頁： 9403-9407 2000年10月

記述言語：英語掲載種別：研究論文（学術雑誌）

H atoms produced by the gamma -ray irradiation of solid para-H-2 (p-H-2) and solid normal-H-2 (n-H-2) decay gradually when the irradiated sample is stored at 4.2 K. ortho-H-2 (o-H-2) molecules at the sites nearest an H atom in solid n-H-2 convert to p-H-2 molecules by interacting with the H atom. H atoms in solid H-2 decay by the process of tunneling diffusion H + p-H-2 --> p-H-2 + H and finally recombine with other I-I atoms. The rate constants for the tunneling reaction were obtained from the decay rates of H atoms in solid H-2 at various concentrations of o-H-2 When solid n-H-2 is stored for 10 h at 4.2 K after gamma -ray irradiation, a number of o-H-2 molecules change into p-H-2 molecules by a catalytic chain reaction induced by mobile H atoms. The G value of the o-H-2 yields from H atoms amounts to 1-2.6 x 10(4). The rate constant for the tunneling reaction ii + p-H-2 --> p-H-2 + H decreases drastically with increasing numbers of o-H-2 molecules, which exist as orientational defects in solid p-H-2. It was concluded that a very small amount of energy (ca. 2 cal mol(-1)) affects the tunneling reaction at very low temperatures.

DOI： 10.1021/jp000440c

An ENDOR study of H atoms in HD solid at 4.2 K 査読有り

J. Kumagai, T. Noda, T. Miyazaki

Chem. Phys. Lett. 321 巻 ( 1-2 ) 頁： 8-12 2000年4月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

An ENDOR spectrum of H atoms in the gamma-ray irradiated HD solid was measured at 4.2 K for elucidating the local environment of HD molecules surrounding ii atoms. The analysis of the ENDOR spectrum indicates that the H atoms are not trapped in substitutional but in pseudo octahedral interstitial sites of HD solid. It is postulated that an H atom, produced by the gamma-irradiation, initially enters the octahedral interstitial site, and then the HD molecules at the first nearest site from the Ii atom are pushed back by zero-point vibration of the ii atom.

DOI： 10.1016/S0009-2614(00)00327-4

Strong resistance of Arabidopsis thaliana and Raphanus sativus seeds for ionizing radiation as studied by ESR, ENDOR, ESE spectroscopy and germination measurement: Effect of long-lived and super-long-lived radicals. 査読有り

J. Kumagai, H. Katoh, T. Kumada, A. Tanaka, S. Tano, T. Miyazaki

Radiat. Phys. Chem. 57 巻 ( 1 ) 頁： 75-83 2000年1月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

Resistance of seeds for ionizing radiation effects on Arabidopsis thaliana and Raphanus sativus seeds were investigated by ESR, ENDOR, ESE spectroscopy and germination measurement. Two types of free radicals, such as long-lived (LL) and super-long-lived (SL) radicals, were produced by the gamma-irradiation in the seeds. More than 90% of the 1 kGy-irradiated-seeds can germinate probably by decreasing the LL radicals by absorbing water. 10 kGy-irradiated-seeds cannot germinate at all probably due to the existence of significant amounts of the SL radicals even after absorbing water.

DOI： 10.1016/S0969-806X(99)00306-0

長寿命ラジカルの生物効果　～イネのUVB照射効果～招待有り

熊谷　純、宮崎哲郎

IGEシリーズ 27 巻頁： 3-12 2000年

Trapping sites of hydrogen atoms in solid HD and D2 : An electron spin echo study 査読有り

T. Kumada, T. Noda, J. Kumagai, Y. Aratono, T. Miyazaki

J. Chem. Phys. 111 巻 ( 24 ) 頁： 10974-10978 1999年12月

記述言語：英語掲載種別：研究論文（学術雑誌）

Trapping sites of H and D atoms in solid HD and D-2 have been determined using electron spin echo (ESE) spectroscopy. It was found that all the H and D atoms are trapped in substitutional sites and that the H atoms push back surrounding HD(D-2) molecules to produce local lattice distortion around the atoms, whereas the D atoms do not. It is expected that the local lattice distortion is produced by zero-point motion of the H atoms whose amplitude is larger than that of host HD(D-2) molecules and that the isotope effect is due to difference in the amplitude between the H and D atoms. The lattice distortion around the H atoms may induce the increase in rate constant for the tunneling reaction D+DH --> D-2+H with the increase in temperature in solid HD reported in Chem. Phys. Lett. 261, 463 (1996).

DOI： 10.1063/1.480461

Differences in the sensitivity to UVB radiation of two cultivars of rice (Oryza sativa L.) based on observation of long-lived radicals 査読有り Open Access

J. Kumagai, H. Katoh, T. Miyazaki, J. Hidema, T. Kumagai

J. Radiat. Res. 40 巻 ( 4 ) 頁： 303-310 1999年12月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

Free radicals with a long lifetime were observed in the leaves of two rice cultivars (Oryza sativa L,.), Sasanishiki (UVB resistant) and Norin-1 (UVB sensitive), by electron spin resonance spectroscopy. The leaves of both cultivars grown with visible light show very similar ESR spectra composed of radical 1 (R1) and radical 2 (R2), which may be attributable to P-700 cation radicals in the reaction center of photosystem I, and tyrosine cation radicals in the reaction center of photosystem II, respectively. The ESR spectrum composed of R1 and R2 radicals in the leaves of Sasanishiki grown under visible light with supplemental UVB was similar to that in the plant grown without supplemental UVB. On the other hand, the amount of R2 radicals in the leaves of Norin-1 grown under visible light with supplemental UVB was significantly smaller than that in the plant grown without supplemental UVB. It is suggested that the loss of R2 radicals in Norin-1 upon UVB irradiation is related to the instability of the plant.

DOI： 10.1269/jrr.40.303

Open Access

Observation of electron bubbles in para-H2-D2 (HD) mixtures by high-resolution ESR spectroscopy 査読有り

T. Kumada, S. Mori, J. Kumagai, Y. Aratono, T. Miyazaki

J. Phys. Chem. A 103 巻 ( 45 ) 頁： 8966-8968 1999年11月

記述言語：英語掲載種別：研究論文（学術雑誌）

A sharp singlet signal assigned to electron bubbles was observed in gamma-irradiated solid para-H-2-D-2 (HD) mixtures by use of high-resolution ESR spectroscopy. The signal was not observed in pure para-H-2 but in the mixtures. This result indicates that the D-2 and HD molecules play an important role in the formation of the electron bubbles in para-H-2. The electron bubbles decay with a half-lifetime of about 2 h, and the decay rate constant at 4.2 K is very close to that at 2.2 K. This result shows that the electron bubbles migrate in the p-H-2 sample via quantum mechanical tunneling.

DOI： 10.1021/jp991650w

Hydrogen radical anions and electron bubbles in solid hydrogen 査読有り

T. Ichikawa, H. Tachikawa, T. Kumada, J. Kumagai, T. Miyazaki

Chem. Phys. Lett. 307 巻 ( 3-4 ) 頁： 283-286 1999年7月

Relation between the helicity and the ESR g-anisotropy of δ-conjugated quantum wires 査読有り

T. Ichikawa, M. Sumita, J. Kumagai

Chem. Phys. Lett. 307 巻 ( 1-2 ) 頁： 81-88 1999年6月

Suppression of the Anderson localization of charge carriers on polysilane quantum wire 査読有り

T. Ichikawa, Y. Yamada, J. Kumagai, M. Fujiki

Chem. Phys. Lett. 306 巻 ( 5-6 ) 頁： 275-279 1999年6月

記述言語：英語掲載種別：研究論文（学術雑誌）

Comparison of the ESR and electronic absorption spectra of the radical ions of poly(cyclohexylmethylsilane) and poly(n-decyl-(s)-2-methylbutylsilane) has shown that the Anderson localization of charge carriers on part of the Si-Si polymer skeleton can be suppressed by replacing the pendant groups with bulky ones. Replacement reduces the flexibility of the polymer skeleton and therefore the dispersion of the resonance energies of the charge carriers between adjacent Si atoms, which suppresses the localization of the charge carriers arising from irregularity of the periodic potential field on the skeleton.

DOI： 10.1016/S0009-2614(99)00487-X

Optical and electronic properties of polysilane radical anions 査読有り

T. Ichikawa, H. Koizumi, J. Kumagai

J. Phys. Chem. B 103 巻 ( 19 ) 頁： 3812-3817 1999年5月

記述言語：英語掲載種別：研究論文（学術雑誌）

Analyses of the electronic absorption spectra and their polarization spectra of the radical anions of permethylated hexa- and octasilane and poly(cyclohexylmethylsilane) in the mixed solvents of nonpolar methylcyclohexane and polar 2-methyltetrahydrofuran at 77 K have revealed that the orbitals of the excess electrons in the radical anions are antibonding pseudo-pi composed of Si 3p(y) atomic orbitals bisecting the Si-Si-Si planes. The near-IR and UV bands of the radical anions are assigned as being due to the excitation of an electron from the SOMO pseudo-pi(3p(y)) to pseudo-pi(3p(y)) and from the HOMO pseudo-pi(3p(x)) to antibonding-sigma(3s), respectively. The near-IR band of the polysilane radical anion shows strong solvatochromic shift, which arises from the localization of the excess electron on a part of the main chain. Localization of the excess electron is proposed to be due to Anderson localization which is induced by the fluctuation of pseudo-pi conjugation arising from the irregularity of the torsional angles of the Si-Si bonds.

DOI： 10.1021/jp9834715

Decay of H₂-anions in solid parahydrogen via two-stage quantum tunneling diffusion processes 査読有り

T. Kumada, N. Kitagawa, S. Mori, J. Kumagai, Y. Aratono, T. Miyazaki

J. Low Temp. Phys. 114 巻 ( 5-6 ) 頁： 413-429 1999年5月

記述言語：英語掲載種別：研究論文（学術雑誌）

Decay mechanism of H-2(-) anions in X(gamma)-irradiated solid para-H-2 (p-H-2) has been studied using high-resolution ESR spectroscopy in the temperature range between 1.3-6.6 K. The results are summarized as follows. First, the decay rate constant of the H-2(-) anions is not proportional to initial yields of reactive species such as cations and H atoms but proportional to the concentration of less-reactive species of HD molecules in p-H-2. This result shows that the decay of the H-2(-) anion is due to the reaction neither with cations nor H atoms but the HD molecules originally contained in the p-H-2 sample at natural abundance. Second, the decay rate constant of the H-2(-) anions increases proportionally with the increase in temperature below 3 K and decreases with the increase in temperature between 3-5 K, although it increases exponentially with the increase in temperature above 5 K. This result indicates that the decay rate constant of the H-2(-) anions is controlled by the rate constant for the diffusion of the H-2(-) anions via one-phonon assisted quantum tunneling below 3 K, two-photon scattered or assisted quantum tunneling between 3-5 K, and thermally-activated process above 5 K.

DOI： 10.1023/A:1021850103903

突然変異や癌化を引き起こす長寿命ラジカルを電子スピンエコー法から探る招待有り査読有り

熊谷　純

放射線化学 67 巻頁： 20-25 1999年

An ENDOR spectrum of H atoms in solid H2 査読有り

T. Kumada, N. Kitagawa, T. Noda, J. Kumagai, Y. Aratono, T. Miyazaki

Chem. Phys. Lett. 288 巻 ( 5-6 ) 頁： 755-759 1998年5月

記述言語：英語掲載種別：研究論文（学術雑誌）

An ENDOR spectrum of H atoms produced in the gamma-ray irradiated solid H-2 was measured at 4.2 K in order to elucidate the structure of the local environment of the H atoms in solid H-2. We found that the H atoms were not trapped in interstitial sites but in substitutional sites of the solid, and almost all the ortho-H(2 )molecules at the first nearest sites from the H atoms converted into para-H-2 molecules. This result shows that the ortho-para conversion is induced by electron spins of the H atoms

DOI： 10.1016/S0009-2614(98)00296-6

Temperature Effect on Selective Tunneling Abstraction Reaction by H Atoms in Neopentane-Alkane Mixtures 4-100K 査読有り

J. Kumagai, T. Kumada, N. KItagawa, N. Morishita, T. MIyazaki

J. Phys. Chem. A 102 巻 ( 17 ) 頁： 2842-2846 1998年4月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

When H atoms are produced by the photolysis of HI or the radiolysis of neo-C5H12 in the neo-C5H12-i-C4H10(2 mol %) mixtures above 40 K, the H atoms react selectively with the solute i-C4H10. The selective reaction is suppressed below 30 K. The reactions have been studied by electron spin resonance and electron spin echo measurements at 4-100 K. The drastic temperature effect on the reaction by H atoms suggests that the H atoms concerned are not hot atoms, but thermal atoms. The thermal H atoms react with the solute alkane by quantum tunneling at low temperature. Temperature effects on the ESR spectra and the spin-lattice relaxation times of the solvent neo-C5H11 radicals and the solute t-C4H9 radicals indicate that local motions of the solute i-C4H10 molecules take place above 40 K, while motions of the solvent neo-C5H12 molecules are severely restricted even at 100 K. It is concluded that the local motions of the solute i-C4H10 assist the tunneling abstraction reaction by H atoms, resulting in the selective reaction with the solute above 40 K.

DOI： 10.1021/jp9801020

Structure of Conduction Electrons on Polysilanes As Studied by Electron Spin-Echo Envelope Modulation Analysis 査読有り

T. Ichikawa, H. Koizumi, J. Kumagai

J. Phys. Chem. B 101 巻 ( 50 ) 頁： 10698-10703 1997年12月

記述言語：英語掲載種別：研究論文（学術雑誌）

The orbital structures of conduction electrons on permethylated oligosilane, Si-8(CH3)(18), and poly(cyclohexylmethylsilane) have been determined by analyzing the electron spin-echo envelope modulation signals of the radical anions of these silanes in a deuterated rigid matrix at 77 K. The conduction electron on permethylated oligosilane is delocalized over the entire main chain, whereas that on poly(cyclohexylmethylsilane) is localized on a part of the main chain composed of about six Si atoms, Quantum-chemical calculations suggest that Anderson localization due to fluctuation of sigma conjugation by conformational disorder of the main chain is responsible for the localization of both the conduction electron and the hole.

DOI： 10.1021/jp972068f

Stabilization of Hydrogen Radical Anions in Solid Hydrogen 査読有り

T.Ichikawa, H. Tachikawa, J. Kumagai, T. Kumada, T. MIyazaki

J. Phys. Chem. A 101 巻 ( 40 ) 頁： 7315-7317 1997年10月

記述言語：英語掲載種別：研究論文（学術雑誌）

The electron spin resonance g-factor of H-2(-) in gamma-irradiated crystalline H-2 was found to be not 2.003 but 2.0023, A novel model has been proposed for explaining the formation and stabilization of Hz-in crystalline H-2. The model assumes H-2(-) to be located at the center of a cavity that has previously been occupied by a trapped electron. The excess electron of H-2(-) is forced to be attached on one H-2 in the cavity due to strong repulsive interactions between the excess electron and H-2 molecules surrounding the cavity. A quantum mechanical calculation shows that an electron trapped in the vacancy of crystalline Hz automatically converts to H-2(-) by drawing one of the surrounding H-2 molecules into the center of the vacancy.

DOI： 10.1021/jp971923s

Direct observation of radical formation by charge recombination

T. Ichikawa, K. Kagei, J. Kumagai, H. Koizumi, H. Yoshida, J. Kubo

Radiat. Phys. Chem. 49 巻 ( 4 ) 頁： 433-436 1997年4月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

Formation of the 2,3,4-trihydronaphtyl radical from the radical cation of tetralin by charge recombination has been studied by electronic absorption spectroscopy. Illumination of the gamma-irradiated glassy alkane solution of tetralin with visible light at 77 K causes electron ejection from the radical anion of tetralin, and the ejected electron recombines with the radical cation to generate the excited tetralin, which then converts to the neutral 2,3,4-trihydronaphtyl radical. The quantum yield of the formation of the neutral radical is approximately the same as that for UV-excited tetralin, which suggests that highly excited states of tetralin are not important for the formation of the neutral radical. The highly excited tetralin molecules generated by charge recombination relax to the first excited state without any chemical reaction, and the scission of a C-H bond takes place under the first excited state.

DOI： 10.1016/S0969-806X(96)00164-8

Electronic Structure of Charge Carriers in a Polysilane Quantum Wire 査読有り

J. Kumagai, H. Yoshida, T. Ichikawa

Nucleonica 42 巻頁： 465 1997年

Interchain Migration of Electrons and Holes in Polysilanes 査読有り

J. Kumagai, H. Tachikawa, H. Yoshida, T. Ichikawa

J. Phys. Chem. 100 巻 ( 42 ) 頁： 16777-16778 1996年10月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

The measurements of the ESR and optical absorption spectra of polysilane radical ions revealed that the hole in the radical cation is delocalized onto the side chains, whereas the excess electron in the radical anion is confined within the silicon main chain. This observation suggests that the side chains hinder the interchain hopping of the charge for the anion but not the cation. Therefore the hole is the primary charge carrier in polysilanes.

DOI： 10.1021/jp961004m

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