Infrared multiphoton dissociation of acetone in a molecular beam

The infrared multiphoton dissociation of acetone has been studied for the f irst time under the collisionless conditions of a molecular beam. A single carbon-carbon bond rupture channel resulting in the formation of an acetyl radical and a methyl radical is the only primary channel observed. The tran slational energy distribution for this channel peaks near zero with an aver age translational energy release of only 2.0 kcal/mol as expected for a rea ction with no exit barrier. Significant secondary decomposition of the acet yl radical to carbon monoxide and methyl radical is also observed. The tran slation energy distribution determined for this channel is peaked well away from zero with an average energy release of 6.1 kcal/mol indicating that i t proceeds on a potential energy surface with a barrier, consistent with pr evious UV experiments. No molecular elimination pathways are observed under the conditions of these experiments.