Molecular Beam Study of Polyatomic Free Radical Reactions. Angular Distributions

摘要

The polyatomic free radicals CH3 and C2H5(R) were produced by thermal dissociation (1500K) 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 three, are small, about 0.5 to 5A squared. 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. (Author)