Tadamasa Shida

Electronic absorption spectra of the radical anions and cations of fullerenes: C60 and C70

Abstract The electronic absorption spectra of the radical ions in the title are observed in γ-irradiated glassy polyatomic matrices at 77 K. The spectral features of all the radical ions are consistent with the available information in the literature which includes photoelectron and resonance Raman spectra of C60 and C70. In addition, the observed spectra compare favorably with the results of CNDO/S calculations.

ESR studies on cation‐radicals of simple olefins and dienes produced in γ‐irradiated frozen solutions of trichlorofluoromethane

Cation radicals of butene‐1, trans and cis butene‐2, isobutene, tetramethylethylene, cyclopentene, cyclohexene, butadiene, 1,3‐pentadiene, cyclopentadiene, 1,3‐ and 1,4‐cyclohexadienes have been produced mostly for the first time in γ‐irradiated frozen matrix of trichlorofluoromethane at 77 K. Well resolved ESR spectra at 77 K or at 130–155 K permit the determination of proton hyperfine coupling constants. Large hyperfine coupling constants of methylene and methyl protons adjacent to π electron systems indicate an extensive hyperconjugation in the cations. The following photoisomerizations are found: butene‐1+→butene‐2+, cyclopentene+→1,3‐pentadiene+, 1,4‐cyclohexadiene+→ 1,3‐cyclohexadiene+, 1,3‐cyclohexadiene+→1,3,5‐hexatriene+. The nonplanar cations of cyclopentene and 1,3‐cyclohexadiene undergo puckering motion in a limitedly warmed matrix. In the warmed matrix, where diffusions of the cation radicals toward unreacted hydrocarbon molecules proceed slowly, proton transfer reactions are induced. Decisiv...

Infrared spectroscopic study of rovibrational states of methane trapped in parahydrogen crystal

The ν3 and ν4 vibrational transitions of methane trapped in solid parahydrogen have been observed by using Fourier transform infrared and high resolution laser spectroscopy. The observed spectrum is interpreted in terms of rovibrational states of the spherical rotor which are subjected to the crystal field splitting. The ν4 band shows extremely sharp lines of a width of ∼0.003 cm−1, while the ν3 band exhibits broader lines of a width of 1 cm−1. The infrared selection rules derived from an extended group theory to take into account the field effect are consistent with the observed spectra. The intermolecular interaction and the field effect in solid parahydrogen are analyzed quantitatively.The ν3 and ν4 vibrational transitions of methane trapped in solid parahydrogen have been observed by using Fourier transform infrared and high resolution laser spectroscopy. The observed spectrum is interpreted in terms of rovibrational states of the spherical rotor which are subjected to the crystal field splitting. The ν4 band shows extremely sharp lines of a width of ∼0.003 cm−1, while the ν3 band exhibits broader lines of a width of 1 cm−1. The infrared selection rules derived from an extended group theory to take into account the field effect are consistent with the observed spectra. The intermolecular interaction and the field effect in solid parahydrogen are analyzed quantitatively.

ESR and optical studies of the radical anion of C60

Abstract The ESR and the electronic adsorption spectrum of the radical anion of C 60 produced by electrolysis were measured at room temperatures and at 77 K. A singlet ESR spectrum with g =1.999 appeared only at 77 K while the electronic absorption spectrum was observed both at room temperatures and at 77 K. The small value of the g factor was associated with the residual orbital angular momentum. The irregular vibrational structure of the electronic absorption of the radical anion in the frozen matrix band was suggested as being due to the Jahn-Teller distortion.

Spectroscopic studies of the radical anion of C60. Detection of the fluorenscence and reinvestigation of the ESR spectrum

Abstract An emission band with a mirror image pattern to the near-IR absorption band is detected for C − 60 produced electrolytically in a solution at room temperatures. The emission band reinforces our previous assignment of the absorption band. The lineshape of the ESR spectrum was reinvestigated to conclude that the isotropic feature at temparatures above 50 K is mainly due to the averaging of the Jahn—Teller distorted structures by pseudo-rotation. The significance of the residual orbital angular momentum is discussed.

Vibrational analysis and calculation of Franck–Condon factors for the vinoxy radical X̃(2A‘) and B̃(2A‘) states

Vibrational analysis and calculation of Franck–Condon factors (FCF) of the vinoxy radical were performed for the two electronic states in the title. Multiconfigurational self‐consistent field (MCSCF) wave functions were used to calculate the optimized geometries and the energy gradients of both states. Vibrational analysis was carried out with the harmonic approximation, and FCFs were calculated taking into account the Duschinsky rotation. The features of the experimental absorption and laser‐induced fluorescence (LIF) spectra were reproduced with the calculated FCFs. Previous analyses of the experimental spectra based on an oversimplified model were critically discussed.

INFRARED SPECTROSCOPIC STUDIES ON PHOTOLYSIS OF METHYL IODIDE AND ITS CLUSTERS IN SOLID PARAHYDROGEN

Methyl iodide is trapped as the monomer and as clusters in the parahydrogen, known as a quantum crystal, at temperatures below about 8 K. UV illumination of the deposited sample at about 5 K causes the dispersal of clusters and the production of the methyl radical, methane, and ethane as evidenced by their infrared absorption spectra. Thermal annealing of the photolyzed sample at temperatures up to 11 K results in the disappearance of the methyl radical, the enhancement of ethane, and the regeneration of methyl iodide. When the initial concentration of the iodide is small, the clusters in the deposited sample are suppressed. For such a sample the UV excitation produces the methyl radical and methane but the formation of ethane is negligibly small. Relevance of the present work to studies of photolysis in gaseous clusters of methyl iodide is discussed.

ESR and optical studies on the cation-radical of pyridine in Aγ-irradiated rigid matrix at low temperatures

Abstract Evidence for the cation-radical of pyridine is obtained by ESR and optical studies of γ-irradiated frozen solutions of pyridine in trichlorofluoromethane at 77 and 4 K. The cation-radical is a σ-type radical, the positive charge residing mostly in the nitrogen lone pair orbital. Consistent spectral data are obtained also for 2-deutero-, 4-deutero-, 2,6-dideutero-, and perdeutero-pyridines.

Absorption Spectra of Dianthracene Anion Radical and Anthracene Dimer Anion

Dianthracene in γ‐irradiated rigid ethereal solutions at 77°K reacts with mobile electrons produced by ionization to give a pair of anthracene molecule and anion which interact weakly to constitute a dimer anion. The dimer anion exhibits spectral features of (i) an extra intermolecular charge resonance band in the near infrared region, (ii) hypochromism in comparison to the free anthracene molecule and anion. The observed spectrum of the dimer can be well accounted for by molecular orbital calculations with the assumption of a sandwich structure for the dimer. In contrast to the mobile electron the matrix‐trapped electron which has less kinetic energy reacts with dianthracene only to give dianthracene anion radicals which show doublet charge resonance bands in the near‐infrared region. The anion is unstable both thermally and optically, and splits to an anthracene molecule and an anion via the dimer anion.

Electronic absorption spectra of cation-radicals of alkanes and CCl4 by a combined optical and ESR studies for γ-irradiated rigid solutions

Abstract The optical absorption spectra of the cation-radicals of various normal and cycloalkanes are confirmed by a parallel ESR and optical measurement. The absorption maxima of the normal alkane cation converge to about 1.2.μ and the absorption thresholds lie in the near IR region, contrary to the expectation from molecular orbital analyses. The optical absorption spectra of the cations are in consistence with the photoelectron and photodecomposition spectra. The apparent difference in the behavior of the alkane cations in the CCl3F and the CCl4 matrices under photo and thermal excitation is consistently accounted for. The cation-radical of CCl4 in both CCl4 and CCl3F matrices is characterized by its optical and ESR spectra.