Direct kinetic measurement of the reaction of the simplest Criegee intermediate with water vapor
Wen Chao, Jun-Ting Hsieh, Chun-Hung Chang, Jim Jr-Min Lin
Science 347, 751 (2015).
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. 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 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.
On the basis of 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 cubic centimeters
per second. This work would help modelers to better constrain the atmospheric
concentrations of CH2OO.