Rate coefficient of the reaction CH₂OO + NO₂ probed with a quantum-cascade laser near 11 μm

The reaction of the simplest Criegee intermediate CH₂OO with NO₂ is considered to be important in atmospheric chemistry because of its prospective contribution to the decay of CH₂OO and the additional source of NO₃, hence its effects on the NO_x and HO_x cycles. The reported rate coefficients of this reaction varied by a factor of 5. Employing a cw quantum-cascade laser with wavelength near 11 μm coupled with Herriott mirrors to probe CH₂OO sensitively, we investigated in detail the reaction CH₂OO + NO₂ under total pressure 5.9-9.7 Torr at 298 K and reported a rate coefficient k_NO = (1.0 ± 0.2) × 10^-12 cm³ molecule^-1 s^-1, about one-seventh the value determined with direct measurements of CH₂OO by Weltz et al. This smaller rate coefficient implies that the title reaction contributes to the atmospheric source of NO₃ and the decay of CH₂OO much less than previously conceived.