Fevering Interstellar Ices Have More CH3OD

Monodeuterated methanol is thought to form during theprestellar core stage of star formation. Observed variations in the CH2DOH/CH3OD ratio suggest that its formation is strongly dependent on thesurrounding cloud conditions. Thus, it is a potential tracer of the physicalconditions before the onset of star formation. A single-point physical modelrepresentative of a typical prestellar core is coupled to chemical models toinvestigate potential formation pathways toward deuterated methanol at theprestellar stage. Simple addition reactions of H and D are not able toreproduce observed abundances. The implementation of an experimentallyverified abstraction scheme leads to the efficient formation of methyl-deuterated methanol, but lacks sufficient formation of hydroxy-deuteratedmethanol. CH3OD is most likely formed at a later evolutionary stage,potentially from H-D exchange reactions in warm ices between HDO (andD2O) 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.

Automated summary

Monodeuterated methanol is believed to be formed during the prestellar core stage of star formation. Variations in the CH2DOH/CH3OD ratio indicate that its formation is strongly influenced by the surrounding cloud conditions, making it a potential tracer of the physical conditions prior to star formation. Chemical models coupled with a representative physical model of a typical prestellar core suggest that simple addition reactions of H and D are not sufficient to explain the observed abundances. Instead, an experimentally verified abstraction scheme is more efficient in producing methyl-deuterated methanol, whereas hydroxy-deuterated methanol formation is insufficient. CH3OD is likely formed at a later evolutionary stage through H-D exchange reactions in warm ices between HDO (and D2O) and CH3OH. The CH2DOH/CH3OD ratio is not suitable as a tracer of the physical conditions during the prestellar stage, but may be better suited as a tracer of ice heating.