Temperature-dependent rate constants for the reactions of the simplest Criegee intermediate (CH₂OO) with acetone (Ac), biacetyl (BiAc), acetylacetone (AcAc), and methylglyoxal (mGly) have been measured over the range 275–335 K using flash photolysis, transient absorption spectroscopy. The measurements were performed at a total pressure of ~80 Torr within a glass jacketed reactor, using N₂ as a bath gas. All reactions are negatively temperature-dependent and show linear Arrhenius plots. The rate constants for these reactions increase in the order Ac < AcAc << BiAc < mGly across the temperature range. At 295 K the rate constants are k_Ac = (4.8±0.4)×10^–13 cm³ s^–1, k_AcAc = (8.0±0.7)×10^–13 cm³ s^–1, and k_BiAc = (1.10±0.09)×10^–11 cm³ s^–1, k_mGly = (3.6±0.15)×10^–11 cm³ s^–1. The reaction of CH₂OO with ketones and aldehydes is a 1,3-dipolar cycloaddition reaction that occurs across the carbonyl double bond, which forms a secondary ozonide via a submerged transition state. The reactivity of these carbonyl compounds with CH₂OO can be understood with frontier molecular orbital theory and predicted using Hammet substituent constants. The faster reacting carbonyls, BiAc and mGly, are major competitive sinks for CH₂OO in the troposphere during the nighttime at lower temperature and relative humidity.

Craig Murray

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