Kinetic studies of oxy-halogen radical systems

Abstract

Chlorine oxide radicals, ClO( 2 II , v " = 0) were obtained as a product of (a) the rapid reaction of Cl with chlorine dioxide at 300°K, Cl + OClO → ClO + ClO, (1) (b) the initiated thermal decomposition of OClO above 320°K, (c) the rapid reaction of Cl with ozone at 300°K, Cl + O 3 → ClO + O 2 . Bromine oxide radicals, BrO ( 2 II , v " = 0), have also been detected in the reaction of bromine atoms with ozone. The decay reaction of ClO radicals was second order in [ClO] at all temperatures studied (294 to 495°K). The decay of [ClO] in the presence of chlorine atom scavengers (H 2 , Br 2 , OClO) has also been studied. The direct reactions of ClO with H 2 (7), and with O 3 (9), were undetectably slow, with k 7 < 10 8.5 and k 9 < 10 9.5 cm 3 mole -1 s -1 at 294°K. The recombination of two ClO radicals probably takes place through a mechanism involving small concentrations of atomic chlorine and the short-lived, ClOO peroxy radical, ClO + ClO → k 2 C1 + ClOO, (2) ClOO + Cl → Cl 2 ( 1 ∑ + g , 3 II Ou+ + O 2 , (3) ClOO + M → Cl + O 2 + M . (4) Rate measurements gave k 2 = (7 ± 2) x 10 11 exp [(— 2500 ± 300)/ RT ] cm 3 mole -1 s -1 from 294 to 495°K. The present values for k 2 are compared with those found previously.