PHOTODISSOCIATION OF ACROLEIN AND PROPYNAL AT 193 NM IN A MOLECULAR-BEAM - PRIMARY AND SECONDARY REACTIONS

The translational energy distribution and the fragment anisotropy for the 193-nm photodissociation products of acrolein H2C = CHCHO and propynal HC = CCHO have been measured with a molecular beam time-of-flight apparatus. For both aldehydes, three distinct dissociation processes have been established: The molecular channel leading to CO + H2C = CH2/HC = CH, the radical channel creating HCO + H2C = CH/HC = C, and the hydrogen channel involving the aldehyde C-H bond fission with the products H + H2C = CHCO/HC = C-CO. Furthermore, the secondary decay processes of the hot photofragments HCO --> H + CO, C2H3 --> C2H2 + H, H2C = CHCO --> C2H3 + CO, and HC = C-CO --> HC = C + CO have been identified, as well as the secondary photodissociations C2H3 + hv --> C2H2 + H and C2H + hv --> C2 + H, which take place within a laser pulse time of approximately 10 ns.