CO product energy distribution in the photodissociation of methylketene and acrolein at 193 nm

CO product vibrational energy distributions in the photodissociation of the two C3H4O isomers, methylketene (CH3CHCO) and acrolein (CH2CHCHO), at 193 nm have been measured by CO laser resonance absorption. The CO from methylketene was found to be vibrationally excited up to v=7, and from acrolein v=6, with average vibrational energies of 3.4±0.3 and 2.7±0.7 kcal/mol, respectively. The similarities observed in the appearance times and in the vibrational energy content of the CO formed in the two systems support our previous conclusion that in the case of acrolein isomerization to methylketene takes place prior to the dissociation process: CH2CHCHO+hν→CH3CHCO*†→CH3CH+CO†. The CO vibrational energy distributions observed in both systems agree closely with the statistical distribution predicted assuming that ethylidene rather than ethylene is formed in the photodissociation reaction.