for methanol (\[\]/\[\]$=6$%, @parise2004first), a species for which the triply deuterated species was also detected in this source.

Chemical simulation {#sec:simul}
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A steady-state model of cold and -depleted clouds was published by @roueff2005interstellar, but their predictions on deuterium enhancement, i.e., 10% for and below 1% for , are significantly underestimated with respect to our findings, which are 87% and 18% for and , respectively.

In an effort to reproduce the observed tendencies of the D/H and spin-state abundance ratios, we have carried out new chemical simulations of (deuterated) amidogen using a model of IRAS16293-2422. We followed the approach described in @Brunken14 and @Harju17b, where more details can be found. Here, we provide only a brief description of the simulations. For the source model we adopted the one used in the above references, where the physical model from @Crimier10, which represents the protostellar core, was extended with a layer of gas representing the molecular cloud that the protostellar system lies in (with $n({\rm H_2}) = 10^4 \, \rm cm^{-3}$ and $T_{\rm dust} = T_{\rm gas} = 10\,\rm K$). The source model is illustrated in Fig.\[fig:IRAS16293\_bestfit\]. We considered a two-stage model, in which the chemical evolution was first calculated over time 