Abundances (upper row) and abundance ratios (lower row) of the various isotopologs as functions of time. The left-hand panels correspond to n(H₂) = 10⁵ cm^-3, while the right-hand panels correspond to n(H₂) = 10⁶ cm^-3. The temperature is set to T_gas = T_dust = 10 K. Solid lines represent calculations using the Hugo et al. (2009) ground-state-to-species rate coefficients, while dashed lines represent calculations using our new fit to the same coefficients (see text).