AB initio vibrational analysis of the Schumann-Runge bands and the neighboring absorption region of molecular oxygen

Abstract

Vibrational wavefunctions are calculated for a number of electronically excited states of molecular oxygen whose potential curves are obtained by large-scale configuration interaction calculation. The calculated oscillator strengths for the transitions to the first eleven vibrational levels corresponding to the discrete portion of the Schumann-Runge band systems are in quite good agreement with experimental data. The theoretical crossing of the 3Πu, 1Πu and 5Π u potential curves leading to predissociation of O2 in its 3Σ-u state is also determined. The three relatively strong hitherto unidentified bands at the high-energy side of the Schumann-Rudge continuum at 9.96, 10.58 and 10.58 eV respectively are shown to result from transitions to the first three vibrational levels of a second mixed valence-Rydberg state of 3Σ-u symmetry determined earlier, calculated at 9.93, 10.29 and 10.63 eV respectively; the observed f values for these lines cannot be explained in the usual way on the basis of Franck-Condon overlaps alone, but rather are only reproduced in the calculations if account is taken of the strong variation of the electronic transition moment with internuclear distance caused by the rapid change from Rydberg to valence character in the region of the 3Σ-u curve crossing. Higher-lying less intense and previously unidentified bands are similarly indicated to result from transitions to a mixed Rydberg-valence 3Πu species. © 1976.