Sensitivity of unimolecular lifetime distributions and energy dependent rate constants to fluctuations in state specific rate constants

Different distribution functions are used to describe fluctuations in state-specific unimolecular rate constants, for states which lie within a narrow energy interval. The effect of these distributions on the reactant population vs time N(τ,S) and the time-dependent unimolecular rate constant k(τ,E) are considered. Comparisons are made with the exponential decay predicts by RRKM (Rice-Ramsperger-Kassel-Marcus) theory of unimolecular kinetics. The collision-averaged unimolecular rate constant k(ω,E) is also determined for each of the distributions of state-specific unimolecular rate constants. Overall, k(ω,E) is found to be relatively insensitive to fluctuations in state-specific unimolecular rate constants.