Dynamics of infrared laser-induced pyrolysis of 1-chloro-1,1-difluoroethane

The dynamics of infrared (IR) laser-induced pyrolysis of CF2ClCH3 has been studied by using a TEA CO2 laser radiation which consisted of a main pulse of 100 ns followed by a tail of 7 mu s containing 70% of total energy. The minimum laser fluence for the effective decomposition of CF2ClCH3 is about 1.5 J cm(-2) at 10P12 laser line (951.19 cm(-1)). Over a moderate range of laser fluence 1.5-7 J cm(-2), the detected product was CF2CH2 generated via the elimination reaction of HCl from CF2ClCH3 and there was no evidence to support HF elimination from CF2ClCH3. The cross sections of photon absorpt ion of CF2ClCH3 are measured as a function of laser fluence. The dependence of decomposition probability on pressure shows collisional dissociation at lower pressure and thermal reaction characteristics at high pressure. A mo del of rate equation has been used to calculate the population distribution s of vibrational levels and decomposition probabilities for three kinds of laser pulse durations, which are in accord with the measured experimental r esults. The model calculation indicates that long laser pulse gives a wide population at the lower vibrational levels and leads to a relatively low de composition probability. (C) 1999 Elsevier Science B.V. All rights reserved .