STATE-TO-STATE DYNAMICS OF PREDISSOCIATION IN OH-AR - EXPERIMENT AND THEORY

Long-lived predissociative levels of OH-Ar which lie as much as 350 cm (-1) above the OH (A (2) Sigma(+), upsilon=0, 1) + Ar dissociation lim its have been identified experimentally and computed based on an adjus ted semiempirical potential-energy surface for OH (A (2) Sigma(+)) + A r. The rotational state distributions of the OH (A (2) Sigma(+)) photo fragments have been probed using a novel variation of the stimulated e mission pumping technique and exhibit a surprising degree of selectivi ty. The highest energetically available OH (a (2) Sigma(+)) rotational channel is always accessed, yet low rotational levels are conspicuous ly absent from the product distributions. Predissociation lifetimes an d product state distributions have also been calculated using the fini te-range scattering wavefunction method. The theoretical results sugge st two main mechanisms for internal rotational predissociation involvi ng Coriolis coupling and the potential anisotropy. Comparison of the e nergies, lifetimes, and product rotational distributions of the OH-Ar predissociative levels observed experimentally with those obtained fro m the theoretical calculations provides a sensitive test of the short- range interaction of this highly anisotropic intermolecular potential- energy surface. Product rotational distributions measured following vi brational predissociation of OH-Ar also give new insight into the shor t-range part of the OH (A (2) Sigma(+)) + Ar intermolecular potential.