Spin–orbit coupling in highly vibrationally excited O2(v) and O2(v=0)–O2(v)

Highly correlated ab initio calculations of the ground and low-lying electronic states of O2 and O4 together with a semi-empirical estimate of the spin–orbit coupling among them have been performed. For the diatomic, our calculations agree well with recent spectroscopic measurements. For the O2(v=0)–O2(v) collision system, avoided crossings allow mixing of the electronic configurations with appreciable spin–orbit coupling into the lowest-lying excited states. As a consequence, spin–orbit transitions can occur at significantly lower vibrational energies of the O2(v) moiety induced by collisions with O2(v=0). This mechanism must be partially responsible for the observed jump in depletion rates of O2(v) determined experimentally.