On the Influence of Uncertainties in Chemical Reaction Rates on Results of the Astrochemical Modelling

With the chemical reaction rate database UMIST95 (Millar et al. 1997) we analyze how uncertainties in rate constants of gas-phase chemical reactions influence the modelling of molecular abundances in the interstellar medium. Random variations are introduced into the rate constants to estimate the scatter in theoretical abundances. Calculations are performed for dark and translucent molecular clouds where gas phase chemistry is adequate. Similar approach was used by Pineau des Forets & Roueff (2000) for the study of chemical bistability. All the species are divided into 6 sensitivity groups according to the value of the scatter in their model abundances computed with varied rate constants. It is shown that the distribution of species within these groups depends on the number of atoms in a molecule and on the adopted physical conditions. The simple method is suggested which allows to single out reactions that are most important for the evolution of a given species.