Influence of transition state resonances on integral cross sections and product rovibrational distributions for the Cl+HCl→ClH+Cl reaction

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Abstract
An accurate quantum scattering calculation for the Cl+HCl→ClH+Cl reaction has been performed. In particular, we study the influence of the lowest transition state resonance on the energy dependence of the state-to-state integral cross sections and product rovibrational distributions. The calculations use a recently developed centrifugal sudden hyperspherical (CSH) coordinate reactive scattering code. The Bondi–Connor–Manz–Römelt semiempirical potential energy surface is employed. All 161 partial waves needed for the convergence of the cross sections are included in the calculations. We find that the resonance perturbs certain reagent and product rotational levels of the vibrational ground state (v=0, j=14–16), as well as all open rotational levels (j=0–8) of the first vibrationally excited state (v=1). Transitions from the ground reagent to the ground product vibrational state, such as v=0, j=15→v′=0, j ′=15, show almost no resonance structure in the integral cross sections; rather direct scattering dominates the partial wave sum. On the other hand, transitions between perturbed v=0 rotational states and any v′=1 rotational state, or between any v=1 state and perturbed v′=0 states, or between any v=1 and any v′=1 state, show a novel resonance feature in the integral cross sections. This novel feature is a sudden smooth ‘‘step’’ in the integral cross section, centered at the resonance energy for the partial wave with zero total angular momentum quantum number (J=0). The step has a width equal to the J=0 resonance width. Sometimes this step is superimposed on a slowly varying background which arises from direct scattering. A quantitative description of these resonant steps in the integral cross sections is developed using a J-shift approximation. Because the resonance influences all rotational states for v=v′=1 in a similar way, there is no significant effect on the product rotational distributions due to the resonance. However, the resonance does produce detectable stepping behavior in the product vibrational distribution.

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