Competing Pathways In The 248 Nm Photodissociation Of Propionyl Chloride And The Barrier To Dissociation Of The Propionyl Radical

Photofragment translational spectroscopy was used to study the photodissociation of propionyl chloride at 248 nm. The crossed laser-molecular beam experiment with VUV photoionization showed two primary dissociation channels, C-Cl bond fission and HCl elimination. Following cleavage of the C-Cl bond, unimolecular dissociation of the propionyl radical produced CH3CH2 and CO. The energy barrier to the CH3CH2CO --> CH3CH2 + CO reaction was estimated to be in the range of 16.3 +/- 1.5 kcal/mol by determining the internal energy distribution of surviving propionyl radicals. No other secondary dissociation channels were observed for the propionyl radical. The HCl elimination channel, previously reported only for the condensed phase of propionyl chloride, was observed as the minor primary dissociation channel in the gas phase. The cofragment to the HCl elimination, CH3CHCO or CH2CH2CO, underwent secondary dissociation to produce CO and CH2CH2 with a significant amount of energy partitioned into translational motion.