Strong Negative Temperature Dependence of the Simplest Criegee Intermediate CH₂OO Reaction with Water Dimer

Abstract

The kinetics of the reaction of CH₂OO with water vapor was measured directly with UV absorption at temperatures from 283 to 324 K. The observed CH₂OO decay rate is second order with respect to the H₂O concentration, indicating water dimer participates in the reaction. The rate coefficient of the CH₂OO reaction with water dimer can be described by an Arrhenius expression <i>k</i>(<i>T</i>) = <i>A</i> exp­(−<i>E</i>_a/<i>RT</i>) with an activation energy of −8.1 ± 0.6 kcal mol^–1 and <i>k</i>(298 K) = (7.4 ± 0.6) × 10^–12 cm³ s^–1. Theoretical calculations yield a large negative temperature dependence consistent with the experimental results. The temperature dependence increases the effective loss rate for CH₂OO by a factor of ∼2.5 at 278 K and decreases by a factor of ∼2 at 313 K relative to 298 K, suggesting that temperature is important for determining the impact of Criegee intermediate reactions with water in the atmosphere