Infrared characterization of the products and the rate coefficient of the reaction between Criegee intermediate CHOO 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 2 I 2 /HCl/N 2 /O 2 irradiated at 308 nm. Five bands near 823.2, 1061.1, 1248.4, 1309.2, and 1359.6 cm −1 were observed and assigned to the gauche -conformer of chloromethyl hydroperoxide (CMHP, CH 2 ClOOH). At a later time of the reaction, absorption bands of H 2 O and formyl chloride (CHClO) at 1782.9 cm −1 were observed; these species were likely produced from the secondary reactions of CH 2 ClO + O 2 → CHClO + HO 2 and OH + HCl → H 2 O + Cl according to temporal profiles of CMHP, H 2 O, and CHClO; formation of CH 2 ClO + OH via decomposition of internally excited CMHP was predicted by theory and both HCl and O 2 are major species in the system. We investigated also the rate coefficient of the reaction CH 2 OO + HCl on probing CH 2 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 HCl = (4.8 ± 0.4) × 10 −11 cm 3 molecule −1 s −1 , is comparable to the only literature value k HCl = (4.6 ± 1.0) × 10 −11 cm 3 molecule −1 s −1 reported by Foreman et al. Infrared spectrum of chloromethyl hydroperoxide, the reaction product of Criegee intermediate CH 2 OO with HCl, was obtained. Secondary products CHClO and H 2 O were also observed. The rate coefficient was determined to be 4.8 × 10 −11 cm 3 molecule −1 s −1 .