HIGH-TEMPERATURE PHOTOCHEMISTRY (HTP) STUDIES OF THE REACTIONS OF GROUND-STATE OXYGEN-ATOMS WITH CHLORO-ETHYLENES

The kinetics of the reactions of O(P-3) atoms with three chloro-ethylenes have been measured using the HTP technique. The following rate coefficient expressions, in cm(3) molecule(-1)s(-1), have been obtained, for: CH2 = CHCl: k(1)(288 - 1233) = 1.6 x 10(-14) (T/K)(0.87) exp(-440 K/T); for CH2 = CCl2: k(2)(295 - 1218) = 6.5 x 10(-16) (T/K)(1.32) exp(-268 K/T); for t-CHCl = CHCl:k(3)(326 - 1164)= 4.5 x 10(-18) (T/K)(1.89) exp(-239K/T). The observations are compared to those on O + C2H4. Below 700 K the temperature dependences of the rate coefficients of these four reactions differ only slightly from each other, consistent with the substituent constants for chlorine substitution. However, the magnitude of the rate coefficients decreases substantially in the sequence k(C2H4)(T) approximate to k(1)(T) approximate to k(2)(T) > k(3)(T), in agreement with the preferential attack of O atoms at the site of the unsubstituted C atoms. While these trends continue at higher temperatures for the first three members of this sequence, a sharp increase has been observed in k(3)(T) above about 700 K. It is shown that this may be attributed to H-atom abstraction from the weakened C-H bond. method for estimating k(T) expressions for further O-atom reactions with chloro-aliphatic compounds is described. The kinetics of reactions of O atoms with chloro-aromatics is briefly considered.