Infrared characterization of the products and the rate coefficient of the reaction between Criegee intermediate CH 2 OO and HCl

Reactions between Criegee intermediates and hydrogen halides might be significant, particularly in the polluted urban atmosphere, because of their large rate coefficients. Employing a Fourier-transform spectrometer in a step-scan mode or a continuous-scan mode, we recorded infrared spectra of transient species and end products in a flowing mixture of CH I /HCl/N /O irradiated at 308 nm. Five bands near 823.2, 1061.1, 1248.4, 1309.2, and 1359.6 cm were observed and assigned to the gauche-conformer of chloromethyl hydroperoxide (CMHP, CH ClOOH). At a later time of the reaction, absorption bands of H O and formyl chloride (CHClO) at 1782.9 cm were observed; these species were likely produced from the secondary reactions of CH ClO + O → CHClO + HO and OH + HCl → H O + Cl according to temporal profiles of CMHP, H O, and CHClO; formation of CH ClO + OH via decomposition of internally excited CMHP was predicted by theory and both HCl and O are major species in the system. We investigated also the rate coefficient of the reaction CH OO + HCl on probing CH OO with a continuous-wave infrared quantum-cascade laser absorption system under total pressure 5.2-8.2 torr at 298 K. The rate coefficient k = (4.8 ± 0.4) × 10 cm molecule s , is comparable to the only literature value k = (4.6 ± 1.0) × 10 cm molecule s reported by Foreman et al.