Molecular beam study of polyatomic free radical reactions. Angular distributions

Abstract

The polyatomic free radicals CH₃ and C₂H₅(R) were produced by thermal dissociation (1500°K) of R₂Cd or R₂Zn. A molecular beam containing about 7%–20% free radicals emerged from the source and collided with a hydrodynamic (nozzle) beam of halogen molecules. Angular distributions of the alkyl halide product were measured with a quadrupole mass spectrometer for the reactions CH₃+Cl₂, Br₂, I₂, ICl (both products), and C₂H₅+Br₂. The reactive scattering is predominantly backwards in the c.m. system and the reaction cross sections, estimated within a factor of 3, are small, about 0.5 to 5 Ų. There is much similarity between these polyatomic free radical reactions and corresponding D atom reactions, except that there is much less forward scattering in the CH₃ cases. The angular distribution of C₂H₅Br is peaked backwards and is remarkably narrow.