Laser spectroscopy of the O₂⁺ molecular ion using a fast ion beam: Fine structure and predissociation lifetimes in the b⁴Σ_g^- state

Abstract

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 example of the potential use of low energy accelerators for FIBLAS work in molecular ion spectroscopy.