COLLISIONAL EFFECTS IN INFRARED MULTIPLE-PHOTON-INDUCED UNIMOLECULAR REACTIONS OF FLUOROETHANE AND TRIFLUOROETHANE

The unimolecular HF elimination reactions of CH3CH2F and CH3CF3 have been used to study the effects of added inert gases (mainly He and N2) upon the product yields from infrared multiple-photon laser (CO2) induced activation. A correlation between laser pulse length and the extent of collisional quenching and/or collisional enhancement was observed. For fluences of <3 J cm-2, addition of inert gas reduced the extent of reaction. For constant pressure of inert gas the degree of quenching increased strongly with increasing length of the laser pulse. On the basis of the results for He, Ar, N2, CH4, and CF4, the relative quenching efficiencies appear to parallel those found in chemical activation studies of CH3CF3. The chemical activation data were extended by studying two new bath gases, HCl and O2. The efficiency of HCl is close to that of CH4, whereas the O2 efficiency resembles that of N2. For high fluence and short pulse irradiation conditions, addition of low pressures of inert gas enhanced the extent of reaction for CH3CF3. The enhancement, which varies with nature of the bath gas, probably is associated with collisional rotational relaxation of the low vibrational levels of CH3CF3. © 1979 American Chemical Society.