BRANCHING IN THE GASEOUS REACTION H+DCL AS A FUNCTION OF COLLISION ENERGY

Branching in the gas-phase reaction H + DCl --> HD + Cl (I) (termed abstraction) and --> HCl + D (II) (exchange) has been measured by monitoring the atomic products Cl and D by resonantly enhanced multiphoton ionization. The collision energy has been varied in the range 1.0-2.4 eV by alteration in the photolytic source of H. Within the error limits, the cross section for abstraction was found to remain constant at 0.16 +/- 0.06 angstrom2. The cross section for exhibited a moderate decrease from 0.6 +/- 0.3 to 0.2 +/- 0.1 angstrom2 with increasing collision energy. These findings concerning the abstraction reaction agree with the results of a quasi-classical trajectory computation, reported here, on the GQQ potential energy surface, the most reliable PES available [Schwenke, D. W.; et al. J. Chem. Phys. 1989, 90, 3110]. The experimental findings for exchange, however, stand in marked contrast to the trajectory results, suggesting that the exchange channel of the GQQ PES may be deficient in the region of high collision energies where the reacting system, en route to exchange, accesses bent intermediate configurations for which ab initio data are lacking.