Experimental study of the dynamics of the H+D2 → HD+D reaction at collision energies of 0.55 and 1.30 eV

We report here experimental measurement of the nascent HD product quantum state distributions for the H+D2 → HD+D reaction. Pulsed laser photolysis of HI in an HI/D2 gas mixture produces hydrogen atoms giving H+D2 collision energies of 0.55 and 1.30 eV. Nanosecond-time-resolved coherent anti-Stokes Raman scattering (CARS) spectroscopy is used to record rotationally and vibrationally resolved spectra of the HD reaction product under nearly single-collision conditions. The spectra are analyzed to determine the nascent, single-collision HD product quantum state distributions. These distributions are compared to the results of related experiments by E. E. Marinero, C. T. Rettner, and R. N. Zare and to the results of recent quasiclassical trajectory calculations of N. C. Blais and D. G. Truhlar. Our results are in qualitative agreement with those of Marinero et al., but there are some quantitative differences. The trajectory calculations yield HD quantum state distributions which are very close to those we have measured. We find that our HD product quantum state distributions are fairly well summarized by a linear surprisal analysis with a rotational surprisal of 3.0 and a vibrational surprisal of 2.6. The quantum state distributions indicate that 71%±1% of the energy available to the products appears in translation, while 19%±2% is in HD rotation, and 10%±2% is in vibration. These results are discussed in terms of the dynamics of the reaction.