Modelled ratio between singly deuterated methanol (CH₂DOH) and non-deuterated methanol (CH₃OH) for several models at four different time steps ranging from 10⁵ yr to 10⁶ yr. We present the varied models that show the largest effects in terms of the amount of methanol in the gas phase: 1D-7 (two-phase model), 1D-8 (only reactive desorption with one product), and 1D-12 (location-dependent cosmic-ray ionisation rate). The black line shows the observed ratio (errors as grey-shaded areas).