The Simplest Criegee Intermediate (H2C=O-O): Isotopic Spectroscopy, Equilibrium Structure, and Possible Formation from Atmospheric Lightning

A number of research groups have recently succeeded in producing the simple carbonyl oxides H2COO and CH3CHOO in sufficient quantity to observe them spectroscopically and to probe the kinetics of their reactions with NO2 and SO2. These latter studies provide evidence that the carbonyl oxides play an important role in the atmosphere, likely contributing to pollutant removal, aerosol formation, and planetary cooling. In this work, Fourier transform microwave and double-resonance spectroscopy are combined with theory to study five isotopic species of H2C=O-O, and a precise equilibrium structure is reported for this ephemeral yet crucial reactive intermediate. In contrast to the other investigations, which have exclusively produced H2C=O-O by halogen chemistry, passing a mixture of methane and excess molecular oxygen through an electrical discharge generates this isomer of H2CO2 with high selectivity, thereby suggesting that the molecule is produced in the direct vicinity of atmospheric lightning.