Fevering Interstellar Ices Have More CH3OD

TL;DR

This study investigates the formation pathways of deuterated methanol in interstellar ices, revealing that CH3OD likely forms later in star formation and that the CH2DOH/CH3OD ratio is more indicative of ice heating than prestellar conditions.

Contribution

It introduces a coupled physical-chemical model showing that simple addition reactions cannot explain observed deuterated methanol ratios, highlighting the importance of H-D exchange reactions in ice heating.

Findings

Simple addition reactions fail to reproduce observed abundances.

H-D exchange reactions likely produce CH3OD during ice heating.

CH2DOH/CH3OD ratio is a tracer of ice heating, not prestellar conditions.

Abstract

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.