Temperature-Dependent Rate Coefficients for the Reaction of CH₂OO with Hydrogen Sulfide

The reaction of the simplest Criegee intermediate CH₂OO with hydrogen sulfide was measured with transient UV absorption spectroscopy in a temperature-controlled flow reactor, and bimolecular rate coefficients were obtained from 278 to 318 K and from 100 to 500 Torr. The average rate coefficient at 298 K and 100 Torr was (1.7 ± 0.2) × 10^-13 cm³ s^-1. The reaction was found to be independent of pressure and exhibited a weak negative temperature dependence. Ab initio quantum chemistry calculations of the temperature-dependent reaction rate coefficient at the QCISD(T)/CBS level are in reasonable agreement with the experiment. The reaction of CH₂OO with H₂S is 2-3 orders of magnitude faster than the reaction with H₂O monomer. Though rates of CH₂OO scavenging by water vapor under atmospheric conditions are primarily controlled by the reaction with water dimer, the H₂S loss pathway will be dominated by the reaction with monomer. The agreement between experiment and theory for the CH₂OO + H₂S reaction lends credence to theoretical descriptions of other Criegee intermediate reactions that cannot easily be probed experimentally.