Benchmark study of the structural and spectroscopic parameters of the hydroxymethyl peroxy (HOCH 2 OO) radical and its decomposition reaction to HO 2 and H 2 CO.

The hydroxymethyl peroxy (HMOO) radical is a product of the oxidation of non-methane hydrocarbons. The present study provides the first accurate computational determination of critical spectroscopic features of the title radical that should aid in its experimental characterization. Structure, energetics, vibrational frequencies, and rotational parameters are reported for the three stable isomers on the ground electronic state of HMOO. While preliminary computations have been carried out using density functional theory as well as second-order Møller-Plesset perturbation theory, for the accurate structural and spectroscopic characterization we made use of coupled-cluster techniques, herewith considering both standard and explicitly correlated methods. The "CCSD(T)/CBS + CV" composite scheme, a state-of-the-art composite approach based on the coupled-cluster theory including single and double excitations together with a perturbative treatment of triples that accounts for extrapolation to the complete basis-set limit as well as core-valence correlation effects, is used to obtain accurate structural and energetic data, in particular for the decomposition reaction to HO2 and H2 CO.