Laser spectroscopy of the O 2 + molecular ion using a fast ion beam: Fine structure and predissociation lifetimes in the b 4 Σ g - state

The predissociation of the b 4Σ g - state of O2 + is reinvestigated by fast ion beam laser spectroscopy (FIBLAS) techniques. The high spectroscopic resolution achieved in the photofragment spectrum, leads to the observation of several hundred lines which are classified in the (3-0), (4-1) and (5-2) bands of the b 4Σ g --a 4II u transition of O2 +. By linewidth analysis, the lifetimes of the v′ = 4 and v′ = 5 levels of the b 4Σ g - state, above the O+(4S) + O(3P) dissociation limit, are studied as a function of the various vibrational, rotational and fine structure quantum numbers. Our results, in good agreement with previous measurements, are interpreted within the framework of a new theoretical a priori study of the predissociation mechanism of O2 +. A complete understanding of the phenomena still requires further experimental investigation and we indicate possible directions of research in this field. As a test experiment, our study of the predissociation of O2 + in the b 4Σ g - state gives a clear exam...