Accurate spectroscopic characterization of the HOC(O)O radical: A route toward its experimental identification

A set of accurate spectroscopic parameters for the detection of the atmospherically important HOC(O)O radical has been obtained by means of state-of-the-art ab initio computations. These include advanced coupled cluster treatments, involving both standard and explicitly correlated approaches, to correctly account for basis set incompleteness and core-valence effects. Geometric parameters for the X̃²A^' and òA^'' states and, for the ground state only, vibrationally corrected rotational constants including quartic and sextic centrifugal distortion terms are reported. The infrared spectrum of the X̃²A^' state has been simulated in the 4000-400 cm^-1 wavenumber interval with an approach based on second order vibrational perturbation theory that allows accounting for anharmonic effects in both energies and intensities. Finally, the vibronic spectrum for the Ã ← X̃ transition has been calculated at three different temperatures in the 9000-3000 cm^-1 energy range with a time-independent technique based on the Franck-Condon approximation.