Conformation-Specific Rate Coefficients of CH3CHOO + HCl Determined with Multiple IR/UV Absorption Probes

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High Resolution Image Download MS PowerPoint Slide Reactions between Criegee intermediates and hydrogen halides significantly impact atmospheric chemistry, particularly in polluted urban environments. We employed a multipass absorption flow cell with four probes to determine the rate coefficient of syn - and anti -CH 3 CHOO + HCl. Infrared quantum-cascade lasers near 883 and 1280 cm –1 provided temporal profiles of syn -CH 3 CHOO and a combination of syn -CH 3 CHOO and the hydrogen-transferred adduct chloroethyl hydroperoxide (CEHP), respectively. A light-emitting diode at 286 nm probed the precursor CH 3 CHI 2, hence [CH 3 CHI] 0 upon photolysis at 248 nm. Laser light at 335 nm probed both syn - and anti -CH 3 CHOO. By modeling the observed temporal profiles, we derived rate coefficients of syn -CH 3 CHOO + HCl and anti -CH 3 CHOO + HCl at 298 K as k HCl syn = (5.1 ± 1.1) × 10 –11 cm 3 molecule –1 s –1 and k HCl anti = (2.9 ± 0.8) × 10 –10 cm 3 molecule –1 s –1, respectively. The latter, previously unreported, is ∼ 5.7 times k HCl syn, highlighting the conformation-specific reactivity.