Theoretical study of the effect of reagent rotation and vibration on the reactions of Cl+H2 and Cl+HD

Quasiclassical trajectory calculations were carried out for the reactions Cl + H-2(nu, J) --> ClH + H and also Cl + HD(nu, J) --> ClH + D or ClD + H for J = 0 to 10 at a relative collision energy E = 6 kcal/mol and also at E = 10 kcal/mol for H,. In addition, the reactive cross-sections for Cl + HD(nu = 0, J = 0) are presented from threshold to 12 kcal/mol, and the ratio of the two products is given from threshold to E = 150 kcal/mol. The goal of the work was to understand the nu and J dependences of both reactive systems as well as the isotope effect for the HD reaction. To help in the analysis calculations were carried out for Cl + H-2(nu = - 1/2, J), i.e., where H-2 had no classical zero-point energy, as well as for Cl + HD(nu = - 1/2, J) and Cl + HD(nu = 1, J). The calculations explain the drop in the cross-sections for both systems as J increases. Zn addition, the isotope effect for Cl + HD(nu = 0, J = 0) is shown to arise from a competition between a vibrational effect that favors the ClH product and an orientational effect that favors the ClD product. The net result is that ClH is favored near threshold but ClD is the preferred product above E = 6 kcal/mol. (C) 1998 Elsevier Science B.V. All rights reserved.