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-ethyle nes have been measured using the HTP technique. The following rate coe fficient 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) ex p(-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 t hese four reactions differ only slightly from each other, consistent w ith the substituent constants for chlorine substitution. However, the magnitude of the rate coefficients decreases substantially in the sequ ence 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 temp eratures for the first three members of this sequence, a sharp increas e has been observed in k(3)(T) above about 700 K. It is shown that thi s may be attributed to H-atom abstraction from the weakened C-H bond. method for estimating k(T) expressions for further O-atom reactions wi th chloro-aliphatic compounds is described. The kinetics of reactions of O atoms with chloro-aromatics is briefly considered.