Abstract
A theoretical study is performed for the photoassociation of metastable helium. Combining short-range, high-level, ab initio calculations for 5Σg/u+ and 5Πg/u symmetries and long-range behaviour, better described in Hund's case (c), potential-energy curves for attractive, 5Σu+ and 5Πg, as well as repulsive, 5Πu and 5Σg+, states of quintet metastable helium molecules dissociating to 2 3S + 2 3P are obtained. Taking into account the atomic spin-orbit couplings, vibrational levels are derived for near-dissociation levels at the 3P2 asymptote. Comparison with results from three recent photoassociation experiments obtained under different conditions (μK temperatures with spin alignment and mK temperatures without) allowed for an assignation of about three quarters of the observed levels. The robustness of the vibrational numbering is confirmed by testing a modification of the short-range potentials.