Shock Wave Study of the Thermal Decomposition of CF 3 and CF 2 Radicals

Abstract

The thermal dissociation reactions CF3 + M = CF2 + F + M (reaction 1) and CF2 + M = CF + F + M (reaction 3) were studied behind shock waves. CF2 radicals were monitored through their UV absorption. By working at very low reactant concentrations, the rate coefficients of the unimolecular processes could be derived. Reaction 1 was investigated between 1600 and 2300 K in the intermediate range of the falloff curves, at 10 times larger bath gas pressures than employed in earlier work (Srinivasan, N. K.; Su, M.-C.; Michael, J. V.; Jasper, A. W.; Klippenstein, S. J.; Harding, L. B. J. Phys. Chem. A 2008, 112, 31). The combination of the two sets of data, together with theoretical modeling, allows one to construct falloff curves and to provide complete representations of the temperature and pressure dependences of the rate coefficients. Reaction 3 was studied in the limiting low-pressure range and, over the range 2900−3800 K, a rate coefficient k3 = [Ar] 1.6 * 10(15)exp(−48040 K/T) cm3 molecule−1 s−1 was obtained. Representations of the rate coefficients over the full falloff curves were again derived by theoretical modeling.