Vibrational state analysis of unrelaxed BaI from the reactions Ba + CH3I and Ba + CH2I2

The reactions Ba + CH₃I → BaI + CH₃ and Ba + CH₂I₂ → BaI + CH₂I 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 + CH₂I₂ is found to be a major reaction pathway with a cross section about twice that for Ba + CH₃I. The relative vibrational populations show for both reactions bell-shaped distributions peaking close to υ = 21 for Ba + CH₃I and υ = 39 for Ba + CH₂I₂. The corresponding average fraction of the total reaction exoergicity that appears as BaI vibration is $\text{f}$_υ = 0.18 for Ba + CH₃I and $\text{f}$_υ = 0.29 for Ba + CH₂I₂. In the case of Ba + CH₃I, 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 + CH₃I reaction to account for this feature of the reaction dynamics.