中央研究院 原子與分子科學研究所

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.

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