Mono-deuterated methanol – a tool to assess the degree of thermal processing of interstellar ices? Beatrice Kulterer 1 , Maria N. Drozdovskaya 1 , Izaskun Jimenez-Serra 2 , Paola Caselli 3 , Silvia Spezzano 3 , Catherine Walsh 4 1 Center for Space and Habitability, Switzerland, 2 Centro de Astrobiología (CSIC-INTA), Spain, 3 Max-Planck-Institut für extraterrestrische Physik, Germany, 4 School of Physics and Astronomy, University of Leeds, United Kingdom Methanol, the simplest complex organic molecule is abundantly detected across the different stages of star formation, but predominantely formed at cold, prestellar stages (1,2) . In addition to the formation of methanol, the deuteration of molecules, where hydrogen is replaced by its heavier isotopologue deuterium, is also favored under cold conditions. Therefore, the ratio of the mono-deuterated methanol isotopologues, CH 2 DOH/CH 3 OD, has been proposed to act as a proxy of the dust temperature in prestellar cores. This hypothesis is motivated by variations of this ratio across the subsequent protostellar stage: values exceeding ten are found for some low- mass protostars (3) , while it approaches unity for high-mass protostellar sources (4) . A low ratio could correspond to warmer core temperatures during the prestellar stage, while a high ratio is speculated to stem from colder core temperatures. However, due to a lack of observations this ratio has not been observationally constrained yet for the prestellar stage. I will show results from a chemical model that explores a first set of experimentally derived formation schemes and implements results from quantum chemical calculations (5,6) for a range of dust temperatures, gas densities and cloud ages resembling conditions at the prestellar stage. Independent of the underlying dust temperature, CH 3 OD formation is inefficient, which questions the idea that the ratio of CH 2 DOH/CH 3 OD is set at the prestellar stage, and a suitable proxy for the dust temperature (7) . The lack of CH 3 OD at the prestellar stage is also supported by new observations of the prototypical prestellar core L1544 conducted with the IRAM 30m telescope and the Greenbank Telescope (8) . To finish, I will present ongoing work that explores additional formation pathways of deuterated methanol, such as the exchange of hydrogen and deuterium between methanol and water, which increases the abundance of CH 3 OD. Experiments have shown that this mechanism becomes effective once temperatures start to exceed 70 K (9,10) , and opens the possibility of utilizing the ratio of CH 2 DOH/CH 3 OD to trace the temperature range that ices experience during the sequential steps of star formation. This study will demonstrate if the ratio of CH 2 DOH/ CH 3 OD is an effective tool to assess the degree of thermal processing that interstellar ices are exposed to during the warm-up phase after the gravitational collapse and during the formation of a protostellar system. References 1. Geppert et al. 2006, Faraday Discussions, 133, 177
2. Watanabe et al. 2004, ApJ, 616, 638W 3. Parise et al. 2006, A&A, 453, 949P 4. Bøgelund et al. 2018, A&A, 615A, 88B 5. Nagaoka et al. 2005, ApJ, 624L, 29N 6. Song et al. 2017, ApJ, 850, 118S 7. Kulterer et al., ACS Earth and Space Chemistry, 6, 1171K
8. Kulterer et al., submitted to A&A 9. Souda 2004, PhRvL, 93, 5502 10. Ratajczak et al. 2009, A&A, 496L, 21R
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