A complete determination of vibrational energy transfer pathways in CH ₂D₂ for states below 3000 cm^-1: A laser induced fluorescence study

Vibrational energy transfer processes in dideuteromethane were studied using a variety of complementary, laser induced fluorescence techniques. The time evolution of population in all infrared active fundamentals, except ν₄ and ν₇, were monitored following three different initial conditions: excess population in ν₇, excess population in a 2000 cm^-1 state, and simultaneous excess population in ν₄ and a 2000 cm^-1 state. These initial perturbations were achieved by irradiating the molecule with the R(22), P(24), and P(38) lines of the 9.6μ CO₂ laser band. Experiments were performed on pure CH₂D₂, CH₂D₂ rare gas, and CH ₂D₂-O₂ mixtures in order to elucidate the vibrational equilibration pathways in the parent molecule. The experimental studies afforded a complete map of the energy transfer pathways between the fundamentals and yielded rate constant for some specific V-V steps. The validity of these conclusions were confirmed by numerical modeling of the system. Theoretical calculations based on the Sharma and Brau, and Schwartz, Slawsky, and Herzfeld formulations were performed to conclude that V-V processes in CH₂D₂ are governed almost exclusively by hard core collisions.