A potential-energy surface study of the 2<i>A</i>1 and low-lying dissociative states of the methoxy radical

Abstract

Low-lying bound and dissociative states of the methoxy radical have been studied at C3v conformations using accurate ab initio quantum chemical techniques. A double-zeta quality basis set augmented with polarization and diffuse functions has been used throughout. The à 2A1 excited state is found to have an equilibrium conformation with RCO=1.614 Å, RCH=1.091 Å, and ΘHCO=102.6°, and the three a1 harmonic frequencies have been calculated (3239, 1308, and 733 cm−1). The following excitation energies have been estimated: à 2A1 ← X̃ 2E vertical excitation, 4.21 eV; à 2A1 → X̃ 2E vertical deexcitation, 3.52 eV; and the ÖX̃ system origin, 3.96 eV. The surface intersections of the à 2A1 state with three low-lying dissociative states (4A2, 2A2, and 4E) have been characterized. The threshold for predissociation has been estimated as 4.47 eV, corresponding to the 2A1–4A2 intersection. The rate of methoxy photolysis is estimated to be too small to warrant inclusion in atmospheric models.