Infrared characterization of the products and the rate coefficient of the reaction between Criegee intermediate CH2OO 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 CH2I2/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, CH2ClOOH). At a later time of the reaction, absorption bands of H2O and formyl chloride (CHClO) at 1782.9 cm(-1) were observed; these species were likely produced from the secondary reactions of CH2ClO + O-2 -> CHClO + HO2 and OH + HCl -> H2O + Cl according to temporal profiles of CMHP, H2O, and CHClO; formation of CH2ClO + 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 CH2OO + HCl on probing CH2OO 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) x 10(-11) cm(3) molecule(-1) s(-1), is comparable to the only literature value k(HCl) = (4.6 +/- 1.0) x 10(-11) cm(3) molecule(-1) s(-1) reported by Foreman et al.

Automated summary

Reactions between Criegee intermediates and hydrogen halides are significant in the polluted urban atmosphere, with observation and assignment of transient species such as chloromethyl hydroperoxide (CMHP). Secondary reactions leading to H2O and formyl chloride (CHClO) were also identified, along with the determination of rate coefficient for the reaction CH2OO + HCl using infrared quantum-cascade laser absorption system under specific conditions.