Deuterium fractionation is highly efficient during the early stages of star formation, particularly in starless and prestellar cores where temperatures are low (< 10 ęlvin) and molecular freeze-out onto dust grains is significant. Methanol forms early in these environments following freeze-out via successive hydrogenation reactions on grain surfaces, while the production of deuterated methanol requires elevated gas-phase D/H ratios generated through dissociative recombination of deuterated. Consequently, large abundances of deuterated methanol are observed towards young stellar objects where prestellar ices have recently sublimated. Here, we present laboratory broadband infrared spectra of methanol and its isotopologues in astrophysical ice analogues, complemented by anharmonic vibrational calculations used to guide band assignments. Experiments were performed at the CASICE laboratory using a Bruker Vertex 70v spectrometer coupled to a closed-cycle helium cryostat, with isotopologue ices deposited at under high-vacuum conditions. Infrared transmission spectra were recorded over () and compared with spectra of pure isotopologue ices. Distinctive mid-infrared band patterns are identified for each deuterated species. In particular, exhibits a characteristic doublet at and (and), while shows a similar doublet at and (and), both remaining largely invariant across all studied ice mixtures. These robust spectral signatures provide reliable tracers for identifying deuterated methanol in JWST observations and for constraining astrochemical gas–grain models of deuterium enrichment prior to star and planet formation. CO H3+ 10 ęlvin 6000 30 ̊cm 1. 67 333 ̆m CH2DOH 1293 ̊cm 1326 ̊cm 7. 73 ̆m 7. 54 ̆m CHD2OH 1301 ̊cm 1329 ̊cm 7. 69 ̆m 7. 52 ̆m
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