Vibrational state analysis of unrelaxed BaI from the reactions Ba + CH 3I and Ba + CH 2I 2

Abstract

The reactions Ba + CH 3I → BaI + CH 3 and Ba + CH 2I 2 → BaI + CH 2I have been investigated by the method of laser-induced fluorescence. Excitation spectra are reported for BaI products formed under single-collision conditions in a “beam-gas” arrangement. The production of BaI for Ba + CH 2I 2 is found to be a major reaction pathway with a cross section about twice that for Ba + CH 3I. The relative vibrational populations show for both reactions bell-shaped distributions peaking close to υ = 21 for Ba + CH 3I and υ = 39 for Ba + CH 2I 2. The corresponding average fraction of the total reaction exoergicity that appears as BaI vibration is f υ = 0.18 for Ba + CH 3I and f υ = 0.29 for Ba + CH 2I 2. In the case of Ba + CH 3I, an estimate for the average relative translational energy of the products, obtained from the primitive angular distribution measurements of Lin, Mims and Herm, can be combined with the average vibrational excitation of BaI to provide evidence that the internal excitation of the methyl radical exceeds that of BaI. A model is discussed which postulates an electron jump in the exit valley of the Ba + CH 3I reaction to account for this feature of the reaction dynamics.