VIBRATIONAL ENERGY-TRANSFER IN THERMAL UNIMOLECULAR SYSTEMS BY THE DIFFUSION CLOUD METHOD - CYCLOPROPANE

Little information is available regarding vibrational energy transfer involving highly excited polyatomic molecules at higher temperatures (≳1000 K). In an earlier paper (ref 6), we described some features of the point source diffusion cloud method which is applied here to the study of the thermal unimolecular isomerization of cyclopropane. The relative collisional energy transfer efficiencies βc for the bath gases He, H2, N2, and CO2 have been determined in the falloff region (k/k∞ ∼ 0.02-0.05) at 975 K. By calibration of absolute rate constants from earlier data, respective values of the average energy down-jump size 〈ΔE〉d were determined; these are approximately 200, 150, 400, and 1100 cm-1, and decrease with increasing temperature to 1175 K; βc also decreases between 975 and 1175 K. These findings have relevance for the interpretation of high temperature gas reactions such as shock tube systems and complement some earlier measurements (ref 7b). © 1979 American Chemical Society.