Time evolution of chemistry with fixed physical parameters in TMC-1

We present a set of time dependent chemical evolution models (based on the UMIST† astrochemistry 2012 code, Woodall et al. (2007); 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. Our computation model included the full UMIST gas-phase reaction network for 467 species Garrod et al. (2008), Graedel et al. (1982). 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). We derive an ammonia age spread for the parts of TMC-1 (Taurus Molecular Cloud-1) that looks more complex than previous estimated showed. Age estimates based on X(NH₃/H₂); X(HCO⁺/H₂) and X(HCO⁺/NH₃) were compared in 3 selected positions, and were found to be very similar (with +/-9% differences).