Temperature dependence of the rate constants for reactions of O(1D) atoms with a number of halocarbons

Abstract

Absolute rate constants for the deactivation of O(1 D) by six halocarbons have been measured over the temperature range 173–343 K using the time resolved decay of the O(1 D→3 P) emission at 630 nm. The rate constants showed no dependence on temperature within the precision of the measurements. The rate constants (in units 10−10 cm3 molecule−1 s−1) are as follows: CCl4,3.1±0.9; CFCl3,2.2±0.7; CF2Cl2,1.45±0.5; CHFCl2,1.9±0.6; CHF2Cl,0.95±0.3; and CF2ClCFCl2,2.0±0.6. These results have been combined with the rate constants for O(1 D) reactions with a number of similar compounds and analyzed according to a simple scheme that assigns a rate constant to each atom attached to carbon. Thus, rate constants for ethane and methane molecules containing hydrogen, fluorine, and chlorine are given by the simple expression k (C n H a F b Cl c ) =0.32a+0.030b+0.74c (in units of 10−10 cm3 molecule−1 s−1). This equation can be used to accurately predict halocarbon rate constants that have not been measured.