On the role of conical intersections and their local topography in the photodissociation of the 1-hydroxyethyl radical

Abstract

The role of conical intersections in the photodissociation of the 1-hydroxyethyl radical is investigated. Two local minima on the 1 2A–2 2A seam of the conical intersection, which correspond to significant stretching of either the O–H or the nonmethyl C–H bond are located, as is an energy minimized intersection on the 2 2A–3 2A seam. The local topography for these conical intersections is determined from the average energy gradient, energy difference gradient and interstate coupling gradient and used to discuss the mechanism of photodissociation. The results are compared with a theoretical study of the hydroxymethyl radical, and are used to explain recent REMPI and photofragment yield spectra. The absence of a REMPI spectrum for the 2 2A state, nominally the 3s Rydberg state, is attributed to a 1 2A–2 2A conical intersection. Time-of-flight spectra in the region of the 2 2A state are discussed, as are spectra in the region of the 3 2A, a 3p Rydberg, state.