The reactive flux correlation function for collinear reactions H + H2, Cl + HCl and F + H2

Abstract

The thermal rate constant for a chemical reaction is given, in its full quantum-mechanical form and without approximation, as the time integral of the flux-flux autocorrelation function. This provides an efficient way for computing rate constants because the correlation function decays to zero in times much shorter than that required for the full state-to-state reactive scattering process, thus requiring one to determine the quantum dynamics of the system only for short times. Reactive flux correlation functions have been calculated for the three title collinear reactions in order to illustrate the various generic behaviour expected for reactive flux correlation functions. H + H2 is an example of simple ‘direct’ dynamics, Cl + HCl has more complex dynamics because of the heavy + light-heavy mass combination, and F + H2 has effects due to the formation of a short-lived collision complex. The reactive flux correlation functions have also been computed using classical mechanics to show the nature of the classical–quantum comparison for them.