Vibrational energy transfer efficiency in a three-channel thermal unimolecular system. Temperature dependence

Thermal isomerization in the three-channel cyclopropane-1t1-2,2d2 system was studied at 823 and 973 K in the presence of Kr and CO2 bath gases. It was found that CO2 is more efficient in energy transfer from the hot cyclopropane than Kr, which is more efficient than He. For the stepladder model of energy transfer, the average energy removed per collision from energized cyclopropane-1t1-2,2d2 by a bath gas 〈ΔE〉 for Kr is 780±90 cm−1 at 823 K and 520±70 cm−1 at 933 K; while for CO2 it is 1220±90 cm−1 at 823 K and 800±70 cm−1 at 973 K. The relative collision efficiency of both bath gases β̄ω also declines with temperature rise. For Kr, β̄ω is 0.17 at 823 K and 0.07 at 973 K; for CO2, β̄ω is 0.40 at 823 K and 0.17 at 973 K. Comparison is made with earlier results. A T−γ(γ∼5.5) temperature dependence fits the existing data for He/cyclopropane sytems and is in accord with the computational deductions of Tardy and Rabinovitch (Ref. 17). For stronger colliders, e.g., Kr and CO2, the temperature dependence of β̄ω should be less than He. A value of ≊1 kcal/mol for the activation energy difference for T and H migration during cyclopropane-1t1-2,2d2 isomerization was confirmed.