Dynamics of the light-atom-transfer reaction Cl + HCl → ClH + Cl: Oscillating reactivity, effect of reagent rotation on reaction cross sections, and rotational excitation of products

The dynamics of the typical light-atom-transfer reaction Cl + HCl → ClH + Cl was studied by three-dimensional quasi-classical trajectory calculations employing LEPS potential energy surfaces with contrasting features. The effect of isotopic substitution (using DCl instead of HCl) and of reagent rotation on the oscillatory behavior of partial cross sections as a function of collision energy was investigated for a potential energy surface that exhibited strong oscillations for Cl + HCl (v = 0; j = 0). The behavior becomes less oscillatory by the isotopic substitution, and the oscillations are quenched drastically by the rotational excitation of the reagents. Based on the results of this study, suggestions are made as to the most promising conditions for observing oscillatory behavior experimentally for H + LH′ reactions. The degree of rotational excitation of the products and the effect of reagent rotation on reaction cross sections were found to be strongly dependent on the nature of the potential energy surface. For one type of surface, reagent rotation promotes the reaction and the products are formed with high rotational energy, while for another type of surface, there is a decline in reactivity between j = 0 and j = 5 or 6, followed by a significant increase, and the products are formed with low rotational energy. The contrasting dynamical results obtained for different potential energy surfaces are discussed in relation to the contrasting features of the surfaces, as indicated by the examination of individual trajectories and in relation to results reported for other H + LH′ systems. The present evidence points to the existence of two different types of potential energy surfaces for H + LH′ reactions: those which we shall call COLD (collinearly directing) since they tend to direct the reactants towards a collinear geometry and form rotationally "cold" products, and those we term HREP since they are of repulsive nature and lead to highly rotationally excited products. Contrasting dynamical results for H + LH′ reactions can be correlated to the contrasting nature of these surfaces.