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Published online by Cambridge University Press: 27 October 2016
We present a set of time dependent chemical evolution models (based on the UMIST† astrochemistry 2012 code, McElroy et al. (2013) for a range of initial physical cloud parameters: 10 K < T < 20 K; 103 cm−3 < n(H2) < 5 ⋅ 104 cm−3; 1 < AV < 10 and with estimated values of scaled interstellar ultraviolet radiation field. We compare our chemical model results with the relative abundances of: CO, CH, OH, HCO+, HCN, HNC, NH3, N2H+ and H2CO molecules. We find significant time dependent variations of the chemical ratios of: X(NH3/H2); X(HCO+/H2) and X(HCO+/NH3). The input physical conditions were taken from Fehér O. et al. (2015) at 16 positions along the TMC-1 dark cloud. The NH3 and HCO+ relative densities based on the observations of Fehér O. et al. (2015) help to find the “chemical age” of the given position in the evolution curves.