On the dissociation of the ozone dication

A mechanism for the dissociation of the ozone dication formed by double ionisation of neutral O-3 is determined by ab initio calculations. The dication ground singlet state is found to have a linear equilibrium geometry that is stable with respect to dissociation to O+ and O-2(+). However, at the Franck-Condon zone for formation of O-3(2+) from the neutral molecule the singlet potential energy surface intersects with a dissociative triplet state. We propose that crossing to this dissociative triplet state can account for the absence of any long-lived O-3(2+) ions in the electron-impact mass spectrum of ozone. Further calculations of the kinetic energy release for the fragmentation of O-3(2+) to O++O-3(+) indicate that considerable vibrational excitation may be present in the O-2(+) ion. (C) 1999 Elsevier Science B.V. All rights reserved.