Photodissociation pathways of 1,1-dichloroacetone

We present a comprehensive investigation of the dissociation dynamics following photoexcitation of 1,1-dichloroacetone (CH ₃COCHCl ₂) at 193 nm. Two major dissociation channels are observed: cleavage of a C-Cl bond to form CH ₃C(O)CHCl + Cl and elimination of HCl. The branching between these reaction channels is roughly 9:1. The recoil kinetic energy distributions for both C-Cl fission and HCl elimination are bimodal. The former suggests that some of the radicals are formed in an excited electronic state. A portion of the CH ₃C(O)CHCl photoproducts undergo secondary dissociation to give CH ₃ + C(O)CHCl. Photoelimination of Cl ₂ is not a significant product channel. A primary C-C bond fission channel to give CH ₃CO + CHCl ₂ may be present, but this signal may also be due to a secondary dissociation. Data from photofragment translational spectroscopy with electron impact and photoionization detection, velocity map ion imaging, and UV-visible absorption spectroscopy are presented, along with G3//B3LYP calculations of the bond dissociation energetics. © 2007 American Chemical Society.