Transition State Resonances in the Reaction Cl + H₂ → HCl + H

This paper discusses converged quantum mechanical scattering calculations for the reaction Cl + H2 → HCl + H and its reverse and analyzes them for the properties of quantized dynamical bottlenecks controlling the total and state-specific microcanonical-ensemble rate constants. These rate constants show clear evidence for quantized transition states. We assign bend and stretch quantum numbers to the transition states for total angular momentum J = 0 with parity P = +1, for J = 1 with P = +1 and −1, and for J = 2 and 6 with P = +1. Then, state-specific densities of reactive states (transition state spectra) are examined to obtain a detailed picture of the reaction. A quantal estimate of the rotational constant, B, for several different transition states is obtained by comparing transition state energies at different values of the total angular momentum. These quantal estimates are in good agreement with the values calculated from the moments of inertia, and this enables us to interpret the results in terms of state-dependent geometries for the individual dynamical bottlenecks. By treating the transition states as poles in the scattering matrix, we also obtain estimates for the lifetimes of the states. The JP-specific rate coefficients, the reactant-state-specific rate coefficients, and the contribution from each transition state to the JP-specific and the reactant-state-specified rate coefficient are also calculated and the trends analyzed. These trends help explain the dependence of the rate coefficient on initial vibrational and rotational quantum numbers.