1(N,PI-STAR) PHOTOCHEMISTRY OF ACETIC-ACID AT 200 NM - FURTHER EVIDENCE FOR AN EXIT CHANNEL BARRIER AND REACTION SELECTIVITY

Acetic acid was photolyzed at 200 nm at low pressure. The nascent OH photofragment was probed by using laser fluorescence excitation to determine its scalar and vector properties. Doppler spectroscopy was used to determine the OH photofragment mean translational energy (E(T)(OH) = 10.4 +/- 1.0 kcal mol-1). Kinematic arguments are presented to demonstrate that acetic acid decomposes via primary C-O single bond fission, with subsequent CH3CO decomposition. Nearly the same mean translational energy is imparted to OH for both 200- and 218-nm photolyses, suggesting the presence of a barrier to product formation in the CH3COOH-->CH3CO + OH exit channel. CD3COOH was photolyzed at 200 and 218 nm to explore the possibility that an enol intermediate plays a role in the dissociation mechanism.