Direct study on the unimolecular decomposition of methoxy radicals: The role of the tunneling effect

Tatsuo Oguchi, Akira Miyoshi*, Mitsuo Koshi, Hiroyuki Matsui

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

16 Scopus citations

Abstract

The unimolecular decomposition of methoxy radicals, CH3O+M → CH2O+H+M (1a), has been directly studied by laser photolysis-laser-induced fluorescence method in the temperature range 610-740 K. Nearly linear pressure dependence of the first-order decay rate was observed in the investigated pressure range (100-450 Torr), and the second-order rate constants were derived for He and N2 buffer gases as: k0(He) = 2.8 x 10-9 exp (-84.3 kJ mol-1/RT) cm3 molecule-1 s-1 and k0(N2) = 4.3 x 10-9 exp(-84.1 kJ mol-1/RT) cm3 molecule-1 s-1, respectively. An RRKM calculation with a semiclassical one-dimensional tunneling treatment showed that the tunneling effect is essentially important in the present experimental conditions. The calculation indicates a non-linear pressure dependence of the rate constant even in the classical low-pressure limiting conditions, which is consistent with the experimental observations. The RRKM model (with threshold energy = 101.7 kJ mol-1) derived by the best fit to the experimental results is in good agreement with the theoretical investigations and the microcanonical rate constants measured by the stimulated emission pumping method.

Original languageEnglish
Pages (from-to)53-60
Number of pages8
JournalBulletin of the Chemical Society of Japan
Volume73
Issue number1
DOIs
StatePublished - 1 Jan 2000

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