Rate constant calculation for HArF → Ar + HF and HKrF → Kr + HF reactions by dual-level variational transition state theory with quantized reactant state tunneling

The rate constants for the gas-phase dissociation of HArF and HKrF through the bending coordinates have been calculated using the dual-level variational transition state theory with quantized reactant state tunneling (QRST) from 20 to 600 K. Tunneling was found to dominate the reaction below 250 K, and the rate constants were found to be approximately temperature independent below 100 K. The deuterium kinetic isotope effects (KIEs) were also calculated in the same temperature range. The calculated KIEs showed dramatic increases below 250 K due to the large differences in the hydrogen and deuterium tunneling rates. Compared to the conventional tunneling method, the QRST predicts appreciably higher rate constants below 50 K and makes the transition from the temperature-dependent domain to the temperature-independent domain more sharply. At the low-temperature asymptote, the QRST predicts 30% to 40% higher KIEs than the conventional tunneling method.