State-to-state measurements of internal rotational predissociation in OH–Ar (A 2Σ+)

Abstract

Internal rotational predissociative levels of OH–Ar (A 2Σ+) have been identified lying up to 350 cm−1 above the OH A 2Σ+ (v=0, 1)+Ar dissociation limit. The predissociative level energies, lifetimes, and OH A 2Σ+ rotational product distributions have been measured. Complexes prepared in many of these predissociative levels are long lived with lifetimes ≥50 ps. A novel variation of stimulated emission pumping has enabled quantitative OH A 2Σ+ rotational distributions to be obtained following OH–Ar predissociation. The OH product distributions are highly selective. The highest energetically available channel is always populated, yet in many cases, low rotational levels are conspicuously absent. The OH–Ar predissociative levels have been assigned nearly good quantum numbers based on a rotational contour analysis of the predissociative features and/or the OH A 2Σ+ rotational product distributions. A two-step mechanism involving Coriolis coupling and the potential anisotropy has been proposed to describe the predissociation process. A comparison between the experimentally measured and theoretically calculated observables provides a guide for further refinements of the OH A 2Σ++Ar potential energy surface.