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

<jats:title>Abstract</jats:title><jats:p>We present a set of time dependent chemical evolution models (based on the UMIST† astrochemistry 2012 code, Woodall <jats:italic>et al</jats:italic>. (2007); McElroy <jats:italic>et al</jats:italic>. (2013) for a range of initial physical cloud parameters: 10 K < T < 20 K; 10<jats:sup>3</jats:sup> cm<jats:sup>−3</jats:sup> < n(H<jats:sub>2</jats:sub>) < 5 · 10<jats:sup>4</jats:sup> cm<jats:sup>−3</jats:sup>; 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 <jats:italic>et al</jats:italic>. (2008), Graedel <jats:italic>et al</jats:italic>. (1982). We compare our chemical model results with the relative abundances of: CO, CH, OH, HCO<jats:sup>+</jats:sup>, HCN, HNC, NH<jats:sub>3</jats:sub>, N<jats:sub>2</jats:sub>H<jats:sup>+</jats:sup> and H<jats:sub>2</jats:sub>CO molecules. We find significant time dependent variations of the chemical ratios of: X(NH<jats:sub>3</jats:sub>/H<jats:sub>2</jats:sub>); X(HCO<jats:sup>+</jats:sup>/H<jats:sub>2</jats:sub>) and X(HCO<jats:sup>+</jats:sup>/NH<jats:sub>3</jats:sub>). 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(NH<jats:sub>3</jats:sub>/H<jats:sub>2</jats:sub>); X(HCO<jats:sup>+</jats:sup>/H<jats:sub>2</jats:sub>) and X(HCO<jats:sup>+</jats:sup>/NH<jats:sub>3</jats:sub>) were compared in 3 selected positions, and were found to be very similar (with ±9% differences).</jats:p>