Masashi Imamura

Pyrene Dimer Cation as Studied by Pulse Radiolysis

Radical cations of pyrene were investigated by the pulse radiolysis technique in solutions of benzonitrile, acetone, and dichloroethane. A 450‐nm absorption band of a pyrene monomer cation was replaced by new bands with maxima at 500, 580, and 750 nm as the pyrene concentration was increased. The latter absorption bands were exclusively assigned to a pyrene dimer cation in equilibrium with the monomer cation at room temperature. Equilibrium constants evaluated were (2.7 ± 0.2) × 102and (5.1 ± 0.5) × 102M−1 at 20°C for benzonitrile and acetone solutions, respectively. The decay processes of both the monomer and dimer cations were discussed. In addition, rate constants of the reactions of both the monomer and dimer cations with triethylamine were found to be 2.7 × 109and 5.4 × 108M−1·sec−1, respectively.

Near infrared absorptions of neon, argon, krypton, and xenon excited diatomic molecules

Two types of transient absorptions due to excited diatomic molecules have been observed for neon, argon, and krypton irradiated with electron beam pulses in following wavelength regions: 8000 to 8200 A and 9000 to 10 300 A for neon, 9500 to 10 000 A and 11 400 to 13 000 A for argon, and 9500 to 10 000 A and 11 600 to 14 000 A for krypton. The first absorptions located at shorter wavelengths consist of several discrete bands and their lifetimes are longer than those of the second absorptions located at longer wavelengths. In addition, the intensities of the second absorptions are much weaker than those of the first absorptions. We have failed to observe the second absorption of xenon, which may be located at longer wavelengths than the observation limit. The time‐dependent changes of absorption spectra suggest the formation of vibrationally and rotationally excited molecules. We attribute the lower state of the first absorption to the lowest triplet state 1u(3Σ+μ) and the upper one to the state 3Πg resulti...

Energy transfer of argon excited diatomic molecules

Argon excited diatomic molecules Ar*2(3J+u)were produced by irradiating argon gas with short electron beam pulses. The kinetic behavior was studied by monitoring the time dependence of the 987.6 nm absorption band due to Ar*2 under various conditions.The method is largely different from the vacuum UV emission spectroscopy used previously in such kinetic studies. Ar*2 was found to be produced by a three‐body reaction with a rate constant of (1.0±0.3) ×10−32 cm 6 sec−1. Then, the rate constants and cross sections of energy transfer were determined for 12 fundamental acceptor molecules. The theoretical formula proposed previously for Penning ionization was applied to energy transfer between Ar*2 cross sections given by the formula have the values comparable to the observed ones.

Optical absorption spectra and kinetic behavior of helium excited diatomic molecule (a 3Σu

The transient absorption spectra of electron‐irradiated 12‐atm helium have been measured in the wavelength region 3000–11 000 A. The observed molecular absorptions correspond to the c 3Σg+←a 3Σu+, e 3Πg←a 3Σu+, and i 3Πg←a 3Σu+ transitions, short‐lived atomic absorptions arising from He*(23S) being observed at several wavelengths. The rotational temperature of He*2(a 3Σ+u, v″=0) produced initially is estimated to be room temperature from the intensity distribution of the P branch. The vibrational deactivation rate of He*2(a 3Σu+, v″=1) depends linearly on helium pressure, the rate constant being 1.0×10−14 cm3 sec−1. The rate constants of the quenching reactions of He*2(a 3Σu+, v″=0) by Ne, Ar, Kr, Xe, H2, N2, O2, CO, NO, N2O, and CO2 have been determined from time‐dependent measurements of the absorption decay. The rate constants range from 0.4×10−10 cm3 sec−1 for Ne to 1.0×10−9 cm3 sec−1 for CO2. An intense emission and absorption were observed at 7772 A in the quenching processes of He*2(a 3Σu+, v″=0) b...

Electronic structures of I2− and I4− ions in γ-irradiated rigid solutions

Abstract Radical-anions of iodine, bromine, and monoiodochloride are produced in γ-irradiated amorphous solids at 77 K, and their electronic and ESR spectra measured. On limited warming of the irradiated solution dimerization by the reaction I 2 − + I 2 → I 4 − occurs to produce the same species as reported by Fornier de Violet et al. The electronic structure of the dimeric anion is discussed in comparison with the monomeric anion.

Lysozyme Dimer Formation on Lysozyme Oxidation with as Studied by Fluorescence Evolution

SummaryLysozyme dimers produced on oxidation of lysozyme with in aqueous solutions exhibit a fluorescence spectrum (λmax=400 nm) closely similar to that of bi-tyrosine. This suggests that the dimer is likely to have a tyrosin–tyrosine bond resulting from the combination of tyrosine phenoxy radicals of two lysozyme molecules. Kinetic studies on dimer formation were made by measuring time-dependent fluorescence after pulsed-electron irradiation over wide pH range. The results lead to the following conclusions. The second-order growth of the dimer fluorescence observed at pH 10·7–12·5 reflects the combination process of the lysozyme radicals, which is rate-determining in the pH range. On the other hand, the first-order growth observed at pH 6·8–10·2 is attributable to the enolization of the keto-form of the dimer. A tentative reaction scheme is proposed for the dimer formation.

Ab initio studies of the β−‐decay in OHT, NH2T, CH3T, and 14CH4

The T→He+ β−‐decay in OHT, NH2T, and CH3T, and the 14C→N+ β−‐decay in 14CH4 are theoretically studied by ab initio SCF‐MO calculations. The ground and excited state daughters and the transition probabilities from the parent to these daughters are calculated with the basis set of the double zeta quality. The potential energy curves of these daughter ions, OHHe+, NH2He+, and CH3He+, are obtained by an ab initio SCF approximation. The correlation of the excited state daughters with the states of XHn + ions is also discussed on the basis of the conservation of the orbital symmetry. In T→He+ β−‐decay, the transition probabilities to the ground state daughters are about 0.61 for all of the parents studied. The main products in the β−‐decays of OHT, NH2T, and CH3T are found to be OH+, NH2+, and CH3+, respectively. The calculated results in CH3T are qualitatively in agreement with the experimental one, but quantitatively the calculation underestimates the production yield of the CH3 + ion. In 14CH4 decay, the tra...

Pulse Radiolysis Studies of Acetone Solutions of Biphenyl and Anthracene: Formation of Ions and Excited Singlet State

The radiolysis of acetone solutions of biphenyl and anthracene has been studied by means of the microsecond‐pulse technique. Transient spectra, as well as the effects of ion scavengers, show the presence of both positive and negative ions of biphenyl and anthracene in irradiated solutions. Assuming that molar extinction coefficients of positive and negative ions are identical, one can determine the yields of ions to be G(biphenyl++biphenyl−) = 1.1 at 0.69M, and G(anthracene++anthracene−) = 1.5 at concentrations above 5 × 10−3M. Decay kinetics of aromatic ions fit the second‐order rate law, which can be ascribed to the charge neutralization reaction between the positive and negative ions; rate constants are found to be k(biphenyl++biphenyl−) = 3.9 × 1011 M−1·sec−1 and k(anthracene++anthracene−) = 2.6 × 1011 M−1·sec−1. The light emitted upon irradiation of acetone solutions of anthracene is anthracene fluorescence; a part of fluorescence is delayed. The relationship between the intensity of fluorescence and...

ESR study on the spatial distribution of radicals trapped in the heavy ion‐irradiated n‐eicosane single crystal

Single crystals of n−eicosane were subjected to the irradiation of helium, carbon, and nitrogen ions accelerated with the cyclotron, and the results were compared with those obtained by 60Co γ‐ray irradiation. Irradiation was carried out at 77 °K. The nature and the spatial distribution of free radicals produced in the crystals were investigated by an ESR technique. The principal radical is –CH2ĊHCH2– (I) and the minor one, CH3ĊHCH2– (II); the linewidth and decay of these radicals were found to be LET‐dependent. The ESR results indicate that radicals are trapped in two regions closely and sparsely; the relative distribution in the two regions is dependent on the LET of radiations used. The mean separation between the radicals trapped in the close proximity was estimated to be approximately 16 A.

Dianion triplet of 9,9′-bianthranyl

Abstract The formation of the dianion triplet of 9,9′-bianthranyl was observed at low temperature. The absorption spectrum of the monoanion implies that an electron is localized in one of anthranyl rings, and in the case of dianion two electrons are localized in both rings. The temperature dependence of the ESR signal at half field suggests that the triplet dianion has many configurations compared with the singlet dianion.