Chemical origin and evolutionary stage of the CH2DOH/CH3OD discrepancy across protostellar masses

Determine which specific chemical process produces the observed discrepancy in the CH2DOH/CH3OD abundance ratio between low-mass and high-mass protostars, and ascertain at which stage of the star-formation sequence (prestellar core, warm-up of ices, or protostellar gas-phase processing) this process operates, in order to understand whether the ratio is set at and inherited from prestellar cores or altered during protostellar evolution.

Background

Methanol deuteration patterns, and specifically the CH2DOH/CH3OD ratio, are used to infer the physical conditions of formation in prestellar cores. Observations show significant discrepancies in this ratio between low-mass protostars (often >3, sometimes >10) and high-mass protostars (≈1 or lower), challenging the assumption of straightforward inheritance of prestellar isotopic ratios.

Resolving whether this discrepancy is rooted in prestellar ice chemistry, subsequent warm-up stage processes, or gas-phase reactions requires identifying both the mechanism and the timing during the star-formation sequence.