The investigation into the broadband infrared spectroscopy of methanol isotopologues reveals fascinating insights into the chemical processes occurring in space. A compelling aspect of this study is the remarkable efficiency of deuterium fractionation during the initial phases of star formation, particularly within starless and prestellar cores. In these environments, characterized by low temperatures (typically below 10 K), significant molecular freeze-out onto dust grains takes place, fostering conditions ripe for various chemical reactions.
As carbon monoxide (CO) freezes out, methanol begins to form through a series of hydrogenation reactions that occur on the surfaces of these grains. Notably, the synthesis of deuterated methanol necessitates higher ratios of deuterium to hydrogen in the gas phase, which arise from the dissociative recombination of deuterated H3+ ions. This process explains why we observe substantial quantities of deuterated methanol in young stellar objects, where prestellar ices have recently undergone sublimation, transitioning back into the gas phase.
In our research, we provide laboratory-based infrared spectra of both methanol and its various deuterated isotopologues, carefully analyzing them in astrophysical ice analogues. These experiments were conducted at the CASICE laboratory using a Bruker Vertex 70v spectrometer paired with a closed-cycle helium cryostat. The isotopologue ices were deposited at a brisk temperature of 10 K under high-vacuum conditions to ensure accuracy in our measurements.
The infrared transmission spectra collected spanned a range from 6000 to 30 cm-1 (or 1.67 to 333 micrometers) and were meticulously compared against spectra obtained from pure isotopologue ices. Each deuterated species exhibited unique mid-infrared band patterns that are clearly identifiable. For instance, CH2DOH presents a distinctive doublet at wavenumbers 1293 and 1326 cm-1 (7.73 and 7.54 micrometers, respectively), while CHD2OH displays a similar doublet at 1301 and 1329 cm-1 (7.69 and 7.52 micrometers). Remarkably, these spectral features remained largely stable across all ice mixtures examined.
These strong spectral signatures serve as reliable indicators for detecting deuterated methanol in observations from the James Webb Space Telescope (JWST) and play a critical role in refining astrochemical models concerning gas-grain interactions and deuterium enrichment prior to the formation of stars and planets.
This research was authored by Adam Vyjidak, Barbara Michela Giuliano, Pavol Jusko, Heidy M. Quitian-Lara, Felipe Fantuzzi, Giuseppe A. Baratta, Maria Elisabetta Palumbo, and Paola Caselli. The manuscript spans 15 pages and includes 15 figures, 14 tables, and 5 appendices, and has been accepted for publication in Astronomy and Astrophysics (A&A). The study touches on subjects related to the astrophysics of galaxies and solar and stellar astrophysics, and can be cited as arXiv:2602.03651 [astro-ph.GA]. For those intrigued by astrobiology and astrochemistry, further exploration into these findings could illuminate our understanding of the cosmic origins of complex molecules.
