overpredict the $o$- column density. None of the parameter combinations we explored lead to the observed level for the / ratio. The chemical model predicts that most of the column originates near the edge of the protostellar core, where the temperature in the source model ($\sim$14K at the very edge, rising inward; cf. Fig.\[fig:IRAS16293\_bestfit\]) inhibits production with respect to . Indeed, a / ratio of unity or above can be produced by the chemical model if the gas is sufficiently dense ($n({\rm H_2}) \gtrsim 10^5 \, \rm cm^{-3}$) and cold ($T \sim 10 \, \rm K$), suggesting that our two-phase approach to the core modelling is inadequate for the modelling of amidogen chemistry, and that a substantial amount of time (of the order of $10^6 \, \rm yr$) is required in the pre-stellar phase for the / ratio to increase to the observed level. We stress that in the present work, we did not carry out radiative transfer simulations of the amidogen absorption lines, and therefore the comparison of the modelled column densities against the observed ones does not take into account any excitation effects. We will present an in-depth comparison of the model versus the observations in an upcoming 