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Conformation-Specific Rate Coefficients of CH3CHOO + HCl Determined with Multiple IR/UV Absorption Probes
Tang-Yu Kao1, Chen-An Chung1, Yuan-Pern Lee1,2
1Department of Applied Chemistry and Institute of Molecular Science, National Yang Ming Chiao Tung University, Hsinchu 300093, Taiwan.
Abstract:
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-CH3CHOO + HCl. Infrared quantum-cascade lasers near 883 and 1280 cm-1 provided temporal profiles of syn-CH3CHOO and a combination of syn-CH3CHOO and the hydrogen-transferred adduct chloroethyl hydroperoxide (CEHP), respectively. A light-emitting diode at 286 nm probed the precursor CH3CHI2, hence [CH3CHI]0 upon photolysis at 248 nm. Laser light at 335 nm probed both syn- and anti-CH3CHOO. By modeling the observed temporal profiles, we derived rate coefficients of syn-CH3CHOO + HCl and anti-CH3CHOO + HCl at 298 K as kHClsyn = (5.1 ± 1.1) × 10-11 cm3 molecule-1 s-1 and kHClanti = (2.9 ± 0.8) × 10-10 cm3 molecule-1 s-1, respectively. The latter, previously unreported, is ∼ 5.7 times kHClsyn, highlighting the conformation-specific reactivity.
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