Dynamics of dissociation of propynoic acid from both ground and excited electronic states at 193Â nm

In our previous work we have reported that propynoic acid (propiolic acid, PA) on excitation at 193 nm undergoes the COH bond cleavage generating OH(v, J), and a major fraction (∼70%) of the available energy is partitioned to the relative translation. In this Letter, we attribute this observation to the presence of an exit barrier in the COH bond cleavage from the T1 state of PA. In addition, vibrationally excited CO2 and CO products, as detected by time-resolved infrared fluorescence at 4.3 and 4.72 μm, respectively, are observed. The rise time of the fluorescence at 4.3 μm exhibits strong pressure dependence, which is explained based on formation of highly vibrationally excited CO2 (0, 0, ν3) molecules and their cascading to lower states. Ab initio molecular orbital calculations suggest both CO2 and CO originate from the ground electronic state of PA.