RATE CONSTANTS AND DEUTERIUM KINETIC ISOTOPE EFFECTS FOR METHOXY RADICAL REACTING WITH NO$_2$ AND O$_2$

Abstract

Alkoxy radicals (RO) are important intermediates in the photooxidation of volatile organic compounds due to their great impacts on ozone formation and gas-particle partitioning of stable oxidation products. Methoxy radical (CH$_3$O À?) is the prototype for all alkoxy radicals. The absolute rate constants k$_N_O_2$(T) for reaction of CH$_3$O À? and CD$_3$O À?with NO$_2$ have been measured using laser flash photolysis to generate radicals and laser-induced fluorescence for time-resolved detection. The pressure and temperature dependence for k$_N_O_2$ have been observed over the range 30-700 Torr and 250-335 K. This will be the first direct measurement of k$_N_O_2$ for CH$_3$O À? near ambient pressure and the first ever for CD$_3$O À?.The relative rate constants k$_N_O_2$/k$_O_2$(T) have been measured in an environmental chamber with FTIR detection. This combination enables the first determination of k$_O_2$ (T) for CH$_3$O À? and CD$_3$O À? for $T < 298$ K. The results will also help validate theoretical methods for studying alkoxy + O$_2$ reactions, which are challenging for quantum chemistry.