The excitation of O(1S) and O2 bands in the nightglow: a brief review and preview

Abstract

Recent laboratory and in situ studies of the processes involved in the excitation of O(¹S) and the five strongest systems of molecular oxygen in the terrestrial nightglow are reviewed. In spite of the significant advances that have been made during the last few years, it is not yet possible to reconcile rocket and satellite photometric observations with expectations based on laboratory kinetic data. Even in the most extensively studied O₂ system, the Herzberg-I system, serious discrepancies exist between the kinetic parameters measured in the laboratory and those deduced from the airglow observations. It is only in the case of the O₂ Atmospheric system that the laboratory and in situ studies have converged on a consistent view of the overall excitation mechanism. In the case of the O(¹S) green line, most evidence would now appear to support the Barth mechanism, but progress towards a conclusive identification of the Barth precursor state, or states, is seriously hindered by the inadequacies in current understanding of the molecular oxygen systems.