Correlated product state distributions in the unimolecular reaction of NCNO

Abstract

Following excitation to S1, expansion-cooled NCNO undergoes nonradiative couplings to S0 and predissociates to CN and NO. Doppler profiles of selected CN B 2Σ+←X 2Σ+ rotational lines were recorded using LIF at several excess energies between 0 and 3000 cm−1. This yields NO V,R distributions associated with specific CN(X 2Σ+) rotational states. The profiles can be fit using the statistical PST/SSE model, and the correlated distributions show no evidence of dynamical bias or exit channel barriers. Doppler profiles generated with polarized lasers show little or no spatial anisotropy of recoil velocities, and are fit by anisotropy parameters β∼0, even at excess energies where predicted unimolecular lifetimes are ≤1 ps. Possible causes for the lack of spatial anisotropy are discussed. Analyses of NO fragment LIF spectra obtained at excess energies of 2348 and 2875 cm−1 show a slight preference for the Π(A′) Λ-doublet component for J″≥30.5, suggesting planar dissociation. An in-plane orientation of the singly occupied pπ lobe in NO is to be expected for dissociation on the ground (A′) electronic potential energy surface.