Photoelectron-photofragment coincidence studies of the dissociative photodetachment of O4-

The dissociative photodetachment dynamics of O-4(-) (O-4(-)+ h nu --> O-2 + O-2 + e(-)) have been studied at 532, 355, and 266 nm by triple-coincidence measurements of the energy and angular distributions of the photoelectron and photofragments. The data reveal vibrationally resolved product translational energy distributions and a strong angular correlation between the photoelectron and the photofragments for this direct process. The translational energy distributions show that photodetachment of O-4(-) over this photon energy range occurs to several low-lying repulsive states of O-4, producing O-2 in the ground and low-lying electronically excited states (O-2(X(3)Sigma(g)(-)), O-2(a (1)Delta(g)), and O-2(b (1)Sigma(g)(+))). The partitioning of energy into vibration and rotation of the O-2 products is analyzed in terms of a Franck-Condon model, indicating that the excess electron in O-4(-) is delocalized over two identical O-2 moieties in a symmetric O-4(-) species. A qualitative analysis of the product angular distributions in terms of the electronic structure of O-4(-) is consistent with recent ab initio calculations. (C) 1998 Elsevier Science B.V. All rights reserved.