The intricate study of methanol isotopologues through broadband infrared spectroscopy reveals significant insights into the early stages of star formation. One of the most compelling aspects of this research is the process of deuterium fractionation, which proves to be remarkably efficient in the initial phases of star development. This phenomenon is especially prevalent in starless and prestellar cores, where the temperatures dip below 10 Kelvin. Here, the process of molecular freeze-out onto dust grains plays a crucial role, leading to the formation of complex molecules like methanol.
In these frigid environments, methanol emerges as carbon monoxide (CO) freezes out, undergoing a series of hydrogenation reactions on the surfaces of dust grains. However, to synthesize deuterated methanol—an isotopologue enriched with deuterium—higher gas-phase D/H ratios are essential. These elevated ratios stem from the dissociative recombination of deuterated H3+, a process that occurs under specific conditions. As a result, one can detect large quantities of deuterated methanol around young stellar objects, particularly in areas where prestellar ices have recently sublimated, highlighting the dynamic nature of these celestial environments.
In this study, we present laboratory infrared spectra detailing methanol and its deuterated isotopologues within astrophysical ice analogues. We complement these findings with anharmonic vibrational calculations that help clarify the band assignments of the spectral data. The experiments were conducted at the CASICE laboratory, utilizing a Bruker Vertex 70v spectrometer paired with a closed-cycle helium cryostat. Isotopologue ices were deposited at a chilling temperature of 10 K under high-vacuum conditions, ensuring precise measurement.
We recorded infrared transmission spectra across a range from 6000 to 30 cm-1 (or approximately 1.67 to 333 micrometers) and meticulously compared these with the spectra of pure isotopologue ices. Each deuterated species exhibits unique mid-infrared band patterns. Notably, CH2DOH displays a distinctive doublet at 1293 and 1326 cm-1 (7.73 and 7.54 micrometers), while CHD2OH reveals a similar doublet at 1301 and 1329 cm-1 (7.69 and 7.52 micrometers). Remarkably, these spectral features remain consistent across all the ice mixtures studied, underscoring their robustness.
These identified spectral signatures serve as reliable indicators for detecting deuterated methanol in observations conducted with the James Webb Space Telescope (JWST). Moreover, they are invaluable for refining astrochemical models related to gas-grain interactions and the enrichment of deuterium prior to the formation of stars and planets.
This article presents contributions from a team of researchers: Adam Vyjidak, Barbara Michela Giuliano, Pavol Jusko, Heidy M. Quitian-Lara, Felipe Fantuzzi, Giuseppe A. Baratta, Maria Elisabetta Palumbo, and Paola Caselli.
For those interested in the detailed findings, the document consists of 15 pages, accompanied by 15 figures, 14 tables, and 5 appendices, and has been accepted for publication in Astronomy and Astrophysics (A&A). The subjects tackled in this research fall under the categories of Astrophysics of Galaxies (astro-ph.GA) and Solar and Stellar Astrophysics (astro-ph.SR). For citation, refer to arXiv:2602.03651 [astro-ph.GA]. If you wish to explore further, the submission history shows that this version was uploaded on February 3, 2026.
