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Direct kinetic measurement of the reaction of the simplest Criegee intermediate with water vapor

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Science  01 Jan 2015:
1261549
DOI: 10.1126/science.1261549

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Abstract

Carbonyl oxides or Criegee intermediates are important transient species formed in the reactions of unsaturated hydrocarbons with ozone. Although direct detection of Criegee intermediates has recently been realized, the main atmospheric sink of Criegee intermediates remains unclear. Here, we report ultraviolet absorption spectroscopic measurements of the lifetime of the simplest Criegee intermediate CH2OO at various relative humidity levels up to 85% at 298 Kelvin. An extremely fast decay rate (~ 5000 per second) of CH2OO was observed at high humidity. The observed quadratic dependence of the decay rate on water concentration implied a predominant reaction with water dimer. Based on the water dimer equilibrium constant, the effective rate coefficient of the CH2OO + (H2O)2 reaction was determined to be (6.5 ± 0.8) × 10−12 cm3 s−1. This work would help modelers to better constrain the atmospheric concentrations of CH2OO.

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