Temperature-dependent rate coefficients and theoretical calculations for the OH+Cl2O reaction

Abstract

Rate coefficients k for the OH+Cl2O reaction are measured as a function of temperature (230-370 K) and pressure by using pulsed laser photolysis to produce OH radicals and laser-induced fluorescence to monitor their loss under pseudo-first-order conditions in OH. The reaction rate coefficient is found to be independent of pressure, within the precision of our measurements at 30-100 Torr (He) and 100 Torr (N2). The rate coefficients obtained at 100 Torr (He) showed a negative temperature dependence with a weak non-Arrhenius behavior. A room-temperature rate coefficient of k1(297 K)=(7.5±1.1)× 10-12 cm3 molecule-1 s-1 is obtained, where the quoted uncertainties are 2 σ and include estimated systematic errors. Theoretical methods are used to examine OH⋯OCl2 and OH⋯ClOCl adduct formation and the potential-energy surfaces leading to the HOCl+ClO (1 a) and Cl+HOOCl (1 d) products in reaction (1) at the hybrid density functional UMPW1K/6-311++G(2df,p) level of theory. The OH⋯OCl2 and OH⋯ClOCl adducts are found to have binding energies of about 0.2 kcal mol-1. The reaction is calculated to proceed through weak pre-reactive complexes. Transition-state energies for channels (1 a) and (1 d) are calculated to be about 1.4 and about 3.3 kcal mol-1 above the energy of the reactants. The results from the present study are compared with previously reported rate coefficients, and the interpretation of the possible non-Arrhenius behavior is discussed. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.