Rotational predissociation dynamics of OH–Ar (<i>A</i> 2Σ+) using the finite range scattering wave function method

Abstract

Predissociative resonances of OH–Ar are computed up to 300 cm−1 above the Ar+OH (A 2Σ+, v=0, j=0) asymptote for total (rotational) angular momentum states J≤10. The energies, lifetimes, and OH A 2Σ+ product rotational distributions of the predissociative resonances are calculated using a numerical method based on the ‘‘energy independent integral’’ finite range scattering wave function (FRSW) [J. Chem. Phys. 99, 1057 (1993)]. The FRSW method involves evaluation of the scattering matrix and its energy derivative, both of which are only parametrically dependent on energy. The energy independent matrices are determined from the discrete eigenvectors of the ℒ2 Hamiltonian matrix H, which is obtained in discrete variable representation, and an exact (analytical) eigenfunction of the asymptotic Hamiltonian operator Ĥ0. Many long-lived (≳1 ps) resonances are identified for OH–Ar in J=3 with projections of J onto the intermolecular axis of K=0–3. The resonances are characterized with approximate bend and stretch quantum numbers based on the nodal structure of the wave functions. The predissociative states decay by Coriolis coupling to a lower K state and/or through mixing of OH rotor levels induced by the anisotropy of the interaction potential. States that predissociate by Coriolis coupling are identified by their J-dependent lifetimes and the OH product rotational levels accessed. The influence of potential anisotropy on the predissociative resonances is explored by changing the average intermolecular bond length and degree of intermolecular bending excitation. A comparison of the theoretically calculated resonances with those observed experimentally provides a guide for refinement of the adjusted semiempirical potential energy surface [J. Chem. Phys. 98, 9320 (1993)] used in the computations.