Kinetics theoretical study of the O(3P) + C2H6 reaction on an ab initio-based global potential energy surface

Abstract

Based on a recently developed analytical full-dimensional potential energy surface describing the gas-phase O(3P) + C2H6 reaction (Espinosa-Garcia et al. in Phys Chem Chem Phys 22:22,591, 2020), thermal rate constants and kinetic isotope effects (KIEs) were studied in the temperature range 200–3000 K using three different kinetics tools: variational transition-state theory with multidimensional tunnelling corrections (VTST/MT), ring polymer molecular dynamics (RPMD), and quasi-classical trajectory (QCT) calculations. Except the last method, which failed in the description at low temperatures, as was expected due to its classical nature, the other two methods present rate constants with differences between them of 3% at low temperatures and 25% at high temperatures, simulate the experimental measurements in the intermediate temperature range, 500–1000 K, and are intermediate between two reviews of experimental measurements at low and high temperatures, where the experimental evidence shows differences of a factor of about 5. This result shows that both methods capture quantum effects, such as zero-point energy, tunnelling, and recrossing effects. The kinetics of the title reaction presents a non-Arrhenius behavior, where the activation energy increases with temperature. Two KIEs were analyzed. For the H/D isotopes, the KIE decreases with temperature, from 46.55 to 1.18 in the temperature range 200–3000 K, while the 12C/13C KIE presents values close to unity. Unfortunately, no experimental information is available for comparison.