The ultraviolet photochemistry of condensed-phase acetyl chloride

Abstract Ultraviolet (UV) irradiation of amorphous and crystalline samples of solid acetyl chloride produces metastable HCl · ketene complexes in a 1:1 ratio following S 1 photoexcitation. The HCl · ketene complex is the only product observed following UV irradiation of either amorphous or crystalline samples. The condensed-phase reaction mechanism contrasts starkly with that of the gas phase mechanism that produces Cl and CH 3 CO radicals by prompt photolysis, followed by dissociation of internally excited CH 3 CO to form CO and CH 3 in a non-concerted process.