Ultraviolet Photodissociation Dynamics of the o-Pyridyl Radical

Abstract

Ultraviolet (UV) photodissociation dynamics of jet-cooled o-pyridyl radical (o-C5H4N) was studied in the photolysis region 224-246 nm using the high-n Rydberg atom time-of-flight (HRTOF) technique. The o-pyridyl radicals were produced from 193 nm photolysis of 2-chloropyridine and 2-bromopyridine precursors. The H-atom photofragment yield (PFY) spectrum contains a broad peak in this wavelength region and reveals the UV absorption feature of o-pyridyl for the first time. The translational energy distributions of the H-atom loss product channel, P(ET)'s, peak at ∼7 kcal/mol, and the fraction of average translational energy in the total excess energy, <fT>, is nearly constant at ∼0.18 in the region 224-242 nm. The P(ET) distribution indicates the production of the lowest energy dissociation products, H + cyanovinylacetylene. The H-atom product angular distribution is isotropic. The dissociation mechanism is consistent with unimolecular dissociation of the hot o-pyridyl radical to H + cyanovinylacetylene after internal conversion from the electronically excited state.