Predissociation of the A2Σ+ (v′ = 3) state of the OH radical

Abstract

Predissociation of electronically excited OHA²Σ⁺ (v′ = 3) is studied using velocity-map imaging of the atomic oxygen photofragments. Fine structure yields, angular distributions and alignment parameters are obtained for the O(³P_J), J = 2,1,0 products. Angular distributions for the O³P₀ (J = 0) fragment, which has no angular momentum polarization, agree well with predictions from the angular distribution simulation computer routine by Kim et al. [J. Chem. Phys., 2006, 125, 133316] which calculates the anisotropy of photofragment recoil as a function of dissociation lifetime, excitation frequency, rotational level, and rotational constant. When angular momentum polarization (i.e. non-equilibrium population distributions of the magnetic sublevels) of the atomic fragments is present, the polarization sensitivity of the O(³P_J) (2 + 1) resonance enhanced multiphoton ionization (REMPI) detection scheme used to detect the O(³P_2,1) products affects the measured angular distribution. Strong polarization effects are observed for the O(³P_2,1) products and accounted for in a simple sudden limit model for the photodissociation. In agreement with the sudden limit predictions for pre-dissociation of OHA²Σ⁺ (v′ = 3) through the ⁴Σ⁻ state, strongly aligned O(³P₂) is found to be the major product.