Unimolecular Decomposition of Chemically Activated sec-Butyl Radicals from H Atoms plus cis-Butene-2

Abstract
Chemically activated sec-butyl radicals have been produced at temperatures between —103° and 25°C by reaction of H atoms with cis-butene-2. H atoms were allowed to effuse through a molecular slit into a spherical reactor containing olefine at low pressure. The system resembles the Polanyi diffusion flame, and some solutions for the radial distribution functions of the species involved are given. Disproportionation-recombination ratios for sec-butyl radicals, and for methyl plus butyl radicals, were measured as 0.94 and 0.30 respectively. The ratios of stabilization vs decomposition by C–C rupture for the energized butyl radicals were measured as a function of pressure and temperature. Hydrogen and helium were also used as inert gases. ka the observed rate constant for decomposition is ∼107 sec—1. The energized butyl radicals are closely monoenergetic. The unimolecular decomposition behavior is compared with theory wherein expressions due to Marcus are employed. All vibrational degrees of freedom may be taken as active.

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