Communication: Determination of the molecular structure of the simplest Criegee intermediate CH2OO.

The simplest Criegee intermediate CH2OO was detected in a discharged supersonic jet of a CH2Br2 and O2 gas mixture by Fourier-transform microwave spectroscopy. The experimentally determined rotational constants of CH2OO and its isotopologues enabled us to derive the geometrical structure. The determined OO and CO bond lengths, which are relevant to a discussion on its electronic structure, are 1.345(3) and 1.272(3) Å, respectively. The CO bond length is close to that of a typical double bond and is shorter than that of the OO bond by 0.07 Å, indicating that CH2OO has a more zwitterionic character H2C = O(⊕)-O(⊖) than biradical H2Ċ-O-O.