  Mono-deuterated methanol is thought to form during the prestellar core stage
of star formation. Observed variations in the CH2DOH/CH3OD ratio suggest that
its formation is strongly dependent on the surrounding cloud conditions. Thus,
it is a potential tracer of the physical conditions before the onset of star
formation. A single-point physical model representative of a typical prestellar
core is coupled to chemical models to investigate potential formation pathways
towards deuterated methanol at the prestellar stage. Simple addition reactions
of H and D are not able to reproduce observed abundances. The implementation of
an experimentally verified abstraction scheme leads to the efficient formation
of methyl-deuterated methanol, but lacks sufficient formation of
hydroxy-deuterated methanol. CH3OD is most likely formed at a later
evolutionarymstage, potentially from H-D exchange reactions in warm ices
between HDO (and D2O) and CH3OH. The CH2DOH/CH3OD ratio is not an appropriate
tracer of the physical conditions during the prestellar stage, but might be
better suited as a tracer of ice heating.
