The curvature of the Arrhenius plots predicted by conventional canonical transition-state theory in the absence of tunneling

The reasons for the nonlinearity of the Arrhenius plots of gas-phase reactions are analyzed in detail within the frame of conventional canonical transition-state theory and in the absence of tunneling effects. The purpose is to show how the vibrational normal mode frequencies of reactants and the transition state determine the curvature of an Arrhenius plot. Conventional canonical transition-state theory without tunneling corrections predicts curved Arrhenius plots with an inflexion point that separates the concave (high-temperature range) and convex region (at low temperatures). The frequencies of the transitional modes at the transition-state structure determine the temperature at which an Arrhenius plot presents upward curvature.