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 (3 nu(1)) results in C-H acetylenic and C-D methyl bond rupture in the similar to 243.1 nm photolysis of CD3C drop 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 similar to 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. (C) 2000 American Institute of Physics. [S0021-9606(00)01937-1].