Photofragment translational spectroscopy of allene, propyne, and propyne-d3 at 193 nm

Abstract

The dissociation dynamics of allene, propyne, and propyne-d3 at 193 nm were investigated with photofragment translational spectroscopy. Products were either photoionized using tunable VUV synchrotron radiation or ionized with electron impact. Product time-of-flight data were obtained to determine centre-of-mass translational energy (P(ET)) distributions, and photoionization efficiency (PIE) curves were measured for the hydrocarbon products. The two major product channels evident from this study are atomic and molecular hydrogen loss, with a H:H2 branching ratio of 90:10, regardless of precursor. The P(ET) distribution for each channel is also largely independent of precursor. Both channels appear to occur following internal conversion to the ground electronic state. The propyne-d3 results show that there is extensive isotopic scrambling prior to H(D) atom loss, and that the H:D product ratio is approximately unity. The PIE curves for H(D) atom loss from allene, propyne, and propyne-d3 indicate that the dominant corresponding C3H3 product is the propargyl radical in all cases. There is some evidence from the PIE curves that the dominant C3H2 products from allene and propyne are propadienylidene (H2CCC:) and propargylene (HCCCH), respectively.