Kinetic Studies of Oxy-Halogen Radical Systems

Chlorine oxide radicals, ClO(2II, 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 + O3 → ClO + O2. Bromine oxide radicals, BrO (2II, 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 (H2, Br2, OClO) has also been studied. The direct reactions of ClO with H2 (7), and with O3 (9), were undetectably slow, with k7 < 108.5 and k9 < 109.5 cm3 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 → k2C1 + ClOO, (2) ClOO + Cl → Cl2(1∑+g, 3IIOu+ + O2, (3) ClOO + M → Cl + O2 + M. (4) Rate measurements gave k2 = (7 ± 2) x 1011 exp [(— 2500 ± 300)/RT] cm3 mole-1 s-1 from 294 to 495°K. The present values for k2 are compared with those found previously.