A temperature dependence kinetics study of the reactions of Cl (2<i>P</i>3/2) with O3, CH4, and H2O2

Abstract

The technique of flash photolysis–resonance fluorescence has been utilized to study the temperature dependences of two chlorine atom reactions of considerable fundamental importance to stratospheric chemistry. These reactions have been studied using a wide range of experimental conditions to ensure the absence of complicating secondary processes. The reactions of interest with their corresponding rate constants are expressed in units of cm3 molecule−1 s−1: Cl+O3→ClO O2 (k1), ΔU°298=−164 kJ mol−1, k1 = (3.08±0.30) ×10−11 exp[−(576±60/RT)], (220–350) K; Cl+CH4→CH3+HCl (k2), ΔU°298=−164 kJ mol−1, k2 = (7.44±0.75) ×10−12 exp[−(2437±110/RT)], (218–401) K. In addition, the followong reaction was studied at 300 K: Cl+H2O2→HCl+HO2 (K3), ΔU°298=−56.8 kJ mol−1, k3?5.8×10−13 (±factor 2.0), 300 K. A direct implication of the new rate data is the need to revise downward by a factor of 2.4 to 3 the magnitude of the ozone perturbation predicted by earlier model calculations due to the presence of ClOx species in the stratosphere.