Infrared Characterization of the Products of the Reaction between the Criegee Intermediate CHCHOO and HCl.

The rapid reactions between Criegee intermediates and hydrogen halides play important roles in atmospheric chemistry, particularly in the polluted urban atmosphere. Employing a step-scan Fourier transform spectrometer, we recorded infrared absorption spectra of transient species and end products of the reaction CHCHOO + HCl in a flowing mixture of CHCHI/HCl/O/N irradiated at 308 nm. Bands at 1453.6, 1383.7, 1357.9, 1323.8, 1271.8, 1146.2, 1098.2, 1017.5, 931.5, and 847.0 cm were observed and assigned to the -conformer of chloroethyl hydroperoxide (-CEHP or CHCHClOOH). In addition, absorption bands of HO and acetyl chloride [CHC(O)Cl, at 1819.1 cm] were observed; some of them were produced from the secondary reactions of CHCHClO + O → CHC(O)Cl + HO and OH + HCl → HO + Cl, according to temporal profiles of HO and CHC(O)Cl. These secondary reactions are conceivable because the nascent formation of CHCHClO + OH via decomposition of internally excited CEHP was predicted by theory, and both HCl and O are major species in the system. The nascent formation of CHCHClO + OH appears to be more important than that of CHC(O)Cl + HO, consistent with theoretical predictions. By adding methanol to deplete some -CHCHOO, we observed only -CEHP with a reduced proportion; this observation indicates that the conversion from -CEHP, expected to be produced from -CHCHOO + HCl, to -CEHP is facile. We also estimated the overall rate coefficient of the reaction -/-CHCHOO + HCl to be = (2.7 ± 1.0) × 10 cm molecule s at ∼70 Torr and 298 K; this rate coefficient is about six times the only literature value = (4.77 ± 0.95) × 10 cm molecule s reported for -CHCHOO + HCl by Liu et al., indicating that -CHCHOO reacts with HCl much more rapidly than -CHCHOO.