Shin Sato

A modified LEPS potential energy surface for the F+H2 reaction

Abstract We propose a modified LEPS potential energy surface for the F+H2→FH+H reaction. Quasiclassical trajectory calculations on this surface can approximately reproduce the angular distributions of the products HF (ν=1, 2 and 3) reported by Neumark et al. (J. Chem. Phys. 82 (1984) 3045).

Reaction of ketenes with atomic oxygen

Rate constants for the reaction of atomic oxygen with ketene, and methyl, ethyl, and dimethyl ketene were measured over a temperature range of 230–449 K using the pulse radiolysis resonance absorption system. Over the temperature range of the experiments, the rate data could be fitted by Arrhenius expressions: O+CH2CO, (2.92±0.78)×10−12exp[(−1349±154 cal mol−1)/RT]; O+(CH3)CHCO, (4.79±1.31)×10−12exp[(494.9±163.2 cal mol−1)/RT]; O+(C2H5)CHCO, (5.36±0.83)×10−12exp[(444.6±94.0 cal mol−1)/RT]; O+(CH3)2CCO, (5.92±0.94)×10−12exp[(1131±85 cal mol−1)/RT]; in units of cm3 molecule−1 s−1. The rate constants at room temperature were also determined using a discharge‐flow system coupled to a photoionization mass spectrometer. Rate constants obtained are 0.043±0.04, 1.16±0.13, 1.36±0.11, and 6.04±0.64×10−11 cm−3 molecule−1 s−1 for CH2CO, (CH3)CHCO, (C2H5)CHCO, and (CH3)2CCO, respectively. Several reaction products were analyzed by the photoionization mass spectrometer.

The rate constants for the H+H2 reaction and its isotopic analogs at low temperatures: Wigner threshold law behavior

Variational transition‐state theory rate constants for the H+H2 reaction and its isotopic analogs at very low temperatures have been calculated using the LSTH potential surface. The Wigner threshold law is found to hold quantitatively below 1 K and to within 34% on average at 5 K. The transition‐state theory rate constants are found to be consistent with the requirements of the Wigner threshold law provided that a tunneling probability having the correct threshold behavior is used in calculating the transmission coefficient. Using these calculated rate constants, decay rates of H and D atoms in solid H2, D2, and HD were estimated and compared with experiment. The good agreement found suggests that these decays occur through quantum mechanical tunneling exchange reactions.

The absolute cross sections for quenching of cadmium 53P1 and 53P0 atoms by methane, nitrogen and isotopic hydrogens

Abstract A phase-shift method was used to determine the absolute cross sections for the quenching of Cd( 3 P 1 ) and Cd( 3 P 0 ). The phase difference between the excitation at 326.1 nm and the fluorescence from Cd( 3 P 1 ) atoms was measured as a function of the pressure of the quenching gases. The rate constants for the intramultiplet mixing were also determined for methane, nitrogen and isotopic hydrogens. Isotopic hydrogens were found to produce Cd( 3 P 0 ) from Cd( 3 P 1 ) very efficiently.

Free radicals formed by reaction of silane with hydrogen atoms in rare gas matrices at very low temperatures

The radicals formed by the reaction of SiH4 with H produced by the photolysis of HI in the matrices of Xe and Kr were investigated by electron spin resonance (ESR) spectroscopy at the temperatures between 4.2 and 100 K. The radicals observed were identified as SiH3 and SiH5. The newly observed radical SiH5 is considered as the intermediate of the reaction SiH4+H→SiH3+H2. The radical had two conformers; both were observed in a Xe matrix, while only one was observed in a Kr matrix. The ESR parameters of these radicals were determined by numerical deconvolution of the observed spectra. The hyperfine coupling of 29Si in silyl radicals isolated in Kr was determined accurately by the present method of the radical formation. The value obtained was 189.5 G instead of 266 G previously reported.

Improved calculations of rate constants for the H+H2 reaction and its isotopic analogs at low temperatures

The rate constants for the H+H2 reaction and its isotopic analogs at very low temperatures have been recalculated using variational transition‐state theory including one‐dimensional tunneling corrections on the Marcus–Coltrin path. For the calculation of the tunneling correction, numerical integration was used and compared with the use of the Eckart fitting function. Using these calculated rate constants, the Wigner threshold law was reexamined and decay rates of H and D atoms in solid H2, D2, and HD were reestimated. The qualitative trend with isotopes did not change from that found in previous calculations.

ESR evidence for the ion-molecule reaction of ethylene cation with its neutral parent giving 1-butene cation in low-temperature matrices

Abstract The irradiated halocarbon solutions of ethylene have been investigated by ESR at low temperatures. 1-butene cation was found to be formed immediately after irradiation at 77 K. Upon warming, the cation was changed into a new species, which was assigned to the propagating radical. Possible mechanisms for the reactions were discussed.

Reactions of NH with C2H6 and C3H8 in the liquid phase

Abstract HN 3 was photolyzed in C 2 H 6 or C 3 H 8 solution at the temperature of dry ice—methanol. The main products were N 2 and C 2 H 5 NH 2 or n -C 3 H 7 NH 2 and i -C 3 H 7 NH 2 . NH 3 and H 2 were also formed as minor products. Possible reaction mechanisms are discussed. It is suggested that alkylamine is mainly formed by the insertion of NH(a 1 Δ) into the CH bonds of C 2 H 6 or C 3 H 8

Phase-shift studies of mercury-photosensitized luminescence of ammonia

Abstract Phase angles between the resonance fluorescence at 253.7 nm and the luminescence from the excited complex formed between mercury and ammonia are found to vary with the wavelength of the emission band of the complex. This result is consistent with there being two emitting sources. By measuring the phase difference between the two emission bands, we estimate the lifetime of the emitter of the long wavelength band to be 1.4 μs.

Kinetic isotope effects in the reaction H + C2H4 → C2H5

Abstract The high-pressure limiting rate constants of the reactions between H or D atoms and three isotopic ethylenes have been measured in the temperature range 206–461 K. Practically no isotope effects due to the differences between the ethylenes could be observed. This result does not agree with the prediction recently made by the activated complex theory.