Collision-induced Energy Transfer and Bond Dissociation in Toluene by H2/D2

Energy transfer and bond dissociation of C-H-methyl and C-H-ring in excited toluene in the collision with H-2 and D-2 have been studied by use of classical trajectory procedures at 300 K. Energy lost by the vibrationally excited toluene to the ground-state H-2/D-2 is not large, but the amount increases with increasing vibrational excitation from 5000 and 40,000 cm(-1). The principal energy transfer pathway is vibration to translation (V-T) in both systems. The vibration to vibration (V-V) step is important in toluene + D-2, but plays a minor role in toluene + H-2. When the incident molecule is also vibrationally excited, toluene loses energy to D-2, whereas it gains energy from H-2 instead. The overall extent of energy loss is greater in toluene + D-2 than that in toluene + H-2. The different efficiency of the energy transfer pathways in two collisions is mainly due to the near-resonant condition between D-2 and C-H vibrations. Collision-induced dissociation of C-H-methyl and C-Hring bonds occurs when highly excited toluene (55,000-70,400 cm(-1)) interacts with the ground-state H-2/D-2. Dissociation probabilities are low (10(-5)similar to 10(-2)) but increase exponentially with rising vibrational excitation. Intramolecular energy flow between the excited C-H bonds occurring on a subpicosecond timescale is responsible for the bond dissociation.