Some Observations Concerning Detailed Balance in Association/Dissociation Reactions

Abstract

In this article we discuss the chemical kinetics of reversible association/dissociation reactions at great length. We find that, as long as the characteristic time for internal-energy relaxation is faster (not necessarily much faster) than that for chemical reaction, there will be a period of time, perhaps only late in the reaction but before equilibrium is reached, during which phenomenological rate laws will apply with rate coefficients that satisfy detailed balance. The nonequilibrium factor, fne, originally introduced by Smith, McEwan, and Gilbert (J. Chem. Phys. 1989, 90, 4265−4273) is not a measure of the degree to which detailed balance is satisfied by the association and dissociation rate coefficients. It is simply the fractional contribution to the “long-time” association rate coefficient, kadd, of the slowest-relaxing eigenmode of the system. That is, 1 − fne is the fractional contribution to the same rate coefficient of the internal-energy relaxation modes. The standard practice of taking the d...