Acetylenic C–H and methyl C–D bond fission in photodissociation of vibrationally excited propyne-d3

Vibrational preexcitation of a state containing three quanta of C–H stretch (3ν1) results in C–H acetylenic and C–D methyl bond rupture in the ∼243.1 nm photolysis of CD3C≡CH, in contrast to previous observations of the almost isoenergetic 193 nm photodissociation of propynes. The C–D bond fission is the dominant pathway with a D/H branching ratio of 2.0±0.5 at a combined energy of ∼50 830 cm−1. The average translational energies of D and H atoms are nearly identical, although the C–H acetylenic and C–D methyl bond energies differ quite extensively, pointing to different dynamics on the involved potential energy surfaces.