Influence of uncertainties in the rate constants of chemical reactions on astrochemical modeling results

Abstract

We analyze the influence of errors in the rate constants of gas-phase chemical reactions on the model abundances of molecules in the interstellar medium using the UMIST 95 chemical database. By randomly varying the rate constants within the limits of the errors given in UMIST 95, we have estimated the scatters in theoretical abundances for dark and diffuse molecular clouds. All of the species were divided into six groups by the scatter in their model equilibrium abundances when varying the rate constants of chemical reactions. The distribution of the species in groups depends on the physical conditions. The scatters in the abundances of simple species lie within 0.5–1 order of magnitude, but increase significantly as the number of atoms in the molecule increases. We suggest a simple method for identifying the reactions whose rate constants have the strongest effect on the abundance of a selected species. This method is based on an analysis of the correlations between the abundance of species and the reaction rate constants and allows the extent to which an improvement in the rate constant of a specific reaction reduces the uncertainty in the abundance of the species concerned to be directly estimated.