Photofragmentation of vinyl iodide at 248 nm. Heat of formation of vinyl radical

Abstract

Studies on the photofragmentation of vinyl iodide have been carried out by a photofragment translational energy spectrometer with rotatable pulsed molecular beam crossed with KrF excimer laser beam. TOF spectra of the iodine atom fragments at different angles of molecular beam showed two primary photodissociation channels: C 2H 3I→I*( 2P 1 2 ) + C 2H 3 and C 2H 3I→I( 2P 3 2 ) +C 2H 3 with ratio I*/I = 1.33. The distribution of E c.m., the total translational energy of the recoiling fragments, was then obtained. The extent of the internal excitation of the vinyl radical, E int, was also determined by energy balance. Energy partitioning of the fragments is consistent with the direct impulsive dynamic model and indicates that the photodissociation of vinyl iodide at 248 nm should proceed on a strongly repulsive surface along the CI bond. The bond dissociation energy D CI in vinyl iodide was determined to be 61.9±1.0 kcal/mol according to the maximum translational energy release in the photofragments. The heat of formation of the vinyl radical thus obtained is 67.2±2.0 kcal/mol.