Experimental and Theoretical Kinetics for the H2O+ + H2/D2 → H3O+/H2DO+ + H/D Reactions: Observation of the Rotational Effect in the Temperature Dependence

Thermal rate coefficients for the title reactions computed using a quasi-classical trajectory method on an accurate global potential energy surface fitted to ∼81,000 high-level ab initio points are compared with experimental values measured between 100 and 600 K using a variable temperature selected ion flow tube instrument. Excellent agreement is found across the entire temperature range, showing a subtle, but unusual temperature dependence of the rate coefficients. For both reactions the temperature dependence has a maximum around 350 K, which is a result of H2O+ rotations increasing the reactivity, while kinetic energy is decreasing the reactivity. A strong isotope effect is found, although the calculations slightly overestimate the kinetic isotope effect. The good experiment–theory agreement not only validates the accuracy of the potential energy surface but also provides more accurate kinetic data over a large temperature range.