Photofragment vector correlations and dissociation dynamics in HONO2

Abstract

Doppler-resolved LIF spectroscopy has been used to probe both the scalar and vector properties of the OH(X) fragments generated via HONO₂ photodissociation at 280 nm. The majority of the excess energy is found to reside in the internal modes of the NO₂ sister fragment (〈ƒ_INT〉≈ 0.65) and in fragment translational motion (〈ƒ_T〉≈ 0.29). Analysis of the vector properties of the OH photofragment indicate a parent molecular transition (A′–A′) to an electronic state of A″ character, mediated by ONO out-of-plane vibrational motion. The observed positive sign of the moment describing the correlation between j_OH and v_OH(implying that v and j lie parallel to one another) points to the dominance of N—OH torsional forces during photofragmentation from the HONO₂ excited state, while the small but positive correlation between v_OH and µ(the parent molecular transition dipole) reflects a planar to pyramidal deformation.