論文 - 熊谷　純

Radical ions of oligosilane and polysilane 査読有り

J. Kumagai, T. Ichikawa, H. Yoshida

Radiat. Phys. Chem.   47 巻 ( 3 ) 頁： 497-499   1996年5月

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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）  

In order to elucidate electronic properties of polysilane Si-Si skeleton, the radical ions generated by gamma-irradiation of polycyclohexylmethylsilane and polymethylphenylsilane were studied by ESR and optical absorption methods. The ion radicals of permethyloligosilanes (Si-4 similar to Si-8) have also been studied for comparison. The observed results suggest that the unpaired electron is localized on a limited region of Si-Si skeleton in the polymers and it is delocalized on the whole Si-Si skeleton of the oligomers.

DOI： 10.1016/0969-806X(95)00147-P

Effect of ionizing radiation on polysilane 査読有り

J. Kumagai, K. Oyama, H. Yoshida, T. Ichikawa

Radiat. Phys. Chem.   47 巻 ( 4 ) 頁： 631-636   1996年4月

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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）  

ESR and gel permeation chromatographic measurements of poly(diethylsilane) and poly(cyclohexylmethylsilane) gamma-irradiated at temperatures between 77 K and 300 K were carried out to elucidate the mechanism of radiation-induced degradation of polysilanes. Radical species observed after the irradiation are not silyl-type radicals generated by the cleavage of the Si-Si bond but alkyl radicals generated by the scission of the C-H bond. The G value of the main-chain scission depends strongly on the irradiation temperature and dose. It is proposed that sigma-conjugation along the main chain allows the migration of the radiation energy to the weakest bond in the main chain where the direct scission of the bond is induced.

DOI： 10.1016/0969-806X(95)00066-7

Formation and isomerization mechanisms of M⁺CO₂^-(M=Li, Na)ion-pair complexes. An Abinitio MO and RPKM study 査読有り

H. Tachikawa, Y. Takatori, A. Ohtake, J. Kumagai, H. Yoshida

Theochem.   342 巻   頁： 1-7   1995年10月

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Structures and electronic states of the M(+)CO(2)(-) (M = Li and Na) ion-pairs have been investigated by means of ab initio MO calculations. The potential energy surfaces (PESs) for the ion-pair formation reaction (M + CO2 --> M(+)CO(2)(-)) show that the ground state MCO(2) complex has a van der Waals (vdW) character (M . CO2) at the entrance region in the reaction and an ionic one (M(+)CO(2)(-)) at short M-C distances and that the activation barrier is found at the intermediate region between the vdW and ion-pair states. The wavefunctions of the ion-pair for the low-lying excited states are obtained by the multireference single and double excitation configuration interaction (MR-SD-CI) method. The first and second electronic excitations are characterized by charge-transfer transition from CO2- to Na+ and local excitation within the CO2- moiety in M(+)CO(2)(-) respectively. In order to elucidate the isomerization mechanism of the Li+CO2- ion-pair from C-s to C-2v structures, which was observed by Kafafi et al. (J. Am. Chem. Sec., 105 (1983) 3886), the Rice-Ramsperger-Kassel and Marcus (RRKM) theory is applied to calculate the microcanonical reaction rate along the reaction coordinate. The calculations strongly support their experimental results in which the reaction Li+CO2-(C-s) --> Li+CO2- (C-2v) occurs preferentially on IR irradiation.

Electronic Structure of Oligosilane and Polysilane Radical Cations as Studied by Electron Spin Resonance and Electronic Absorption Spectroscopy 査読有り

J. Kumagai, H. Yoshida, T. Ichikawa

J. Phys. Chem.   99 巻 ( 20 ) 頁： 7965-7969   1995年5月

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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 electron spin resonance (ESR) and the electronic absorption spectra of oligosilane (Si(n)R(n+1)R(n+1)', n = 2 similar to 6) radical cations in a cryogenic solid of a Freon mixture have been compared with those of poly(cyclohexylmethylsilane) and poly(methylphenylsilane) radical cations for elucidating the structure of the SOMO orbital of the radical cations or the HOMO orbitals of the neutral polysilanes, The absorption and ESR spectra of the polymer radical cations are similar to each other and also similar to those of the oligosilane radical cations, which suggests that the unpaired electron of the polymer radical cations is not delocalized all over the Si-Si main chain. The absorption spectra of the polysilane radical cations are composed of a UV and near IR bands which correspond to SOMO --> LUMO and SOMO - 1 --> SOMO, respectively. The oligosilane and the polysilane radical cations show broad isotropic ESR spectra due to hyperfine interactions with side-chain protons. Analysis of the ESR spectra shows that the unpaired electron of the polysilane radical cation is confined to only a part of the polymer chain composed of six Si atoms.

DOI： 10.1021/j100020a019

Electronec Structure of Oligosilane and Polysilane Radical Anions As Studied by Electron Spin Resonance and Electronic Absorption Spectroscopy 査読有り

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

J. Phys. Chem.   98 巻 ( 50 ) 頁： 13117-13122   1994年12月

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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 electron spin resonance (ESR) and the electronic absorption spectra of poly(cyclohexylmethylsilane) and poly(methylphenylsilane) radical anions in a cryogenic 2-methyltetrahydrofuran solid have been compared with those of permethyloligosilanes [Si-n(CH3)(2n+2), n = 4-6] for elucidating the electronic structure of polysilane radical anions. The spectra of the polysilane radical anions are very similar to each other and also to those of the oligosilane radical anions in which an unpaired electron occupies not an antibonding sigma(not asymptotic to)(sp) orbital but a pseudo-pi(p) orbital composed of antibonding Si-Si and antibonding Si-C orbitals. The polysilane radical anions show axially symmetric ESR spectra with g(perpendicular to) = 2.0023 and g(parallel to) = 2.0064 and the electronic absorption spectra composed of UV and near-IR bands. Analysis of the ESR and the absorption spectra shows that the unpaired electron of the polysilane radical anions is not delocalized all over the polymer chain but is confined in only a part of the polymer chain, probably around the elongated Si-Si bond of a branched polymer chain.

DOI： 10.1021/j100101a005