Photodissociation channels and energy partitioning in the photofragmentation of alkyl iodides

Abstract

Studies on the photofragmentation of CH 3I, C 2H 7I, C 3H 7I, and i-C 3H 7I have been carried out using a rotatable pulsed molecular beam crossed with a KrF excimer laser. TOF spectra of the iodine atom fragments show the separation of the primary photodissociation channels I*( 2P 1 2 ) and I( 2P 3 2 . The [I*]/[I] ratios obtained are 2.80, 2.37, 1.61, and 0.96, respectively, by translational energy measurements on the recoiling photofragments. The internal excitation of the alkyl fragments ( E int) is determined by energy balance. The fraction of the available energy, which goes into internal excitation, increases from 12.5% for the I* channel of CH 3I to 64% for both channels of i-C 3H 7I. The bond energies D C-I for methyl and ethyl iodide are 55.0±0.5 and 55.3±1.0 kcal/mol respectively, according to the maximum translational energy release in the I* channel. The origin of the I( 2P 3 2 ) channel (caused by curve crossing) is discussed.