Photodissociation of acetyl chloride: Cl and CH3 quantum yields and energy distributions

Abstract

Jet cooled acetyl chloride is dissociated at 236 nm via excitation of the 1[n, π* (C=O)] transition. Chlorine atom photofragments Cl(2P3/2) and Cl*(2P1/2) are detected using (2+1) multiphoton ionization. The relative Cl* yield φ*=[Cl*]/([Cl]+[Cl*]) is measured to be 0.4±0.02, and the mean translational energy of the Cl atoms is 0.28±0.02 eV. Methyl fragments are also detected following primary dissociation and the internal state distributions are probed using (2+1) multiphoton ionization through the 4pz Rydberg state at 286 nm and the 3pz Rydberg state at 334 nm. The quantum yield for CH3 formation is estimated to be 28%, relative to the CH3 yield from methyl iodide photolysis. A small fraction of the available energy is channeled into methyl fragment angular momentum as the rotational state distribution extends only to N″=5. Our results indicate that CH3CO, generated as a primary photoproduct in the dissociation of acetyl chloride, subsequently decomposes to produce CH3 and CO. Energetic constraints in the mechanism of acetyl chloride dissociation are discussed.