Testing grain surface chemistry : a survey of deuterated formaldehyde and methanol in low-mass Class 0 protostars

By B. Parise, C. Ceccarelli, A. Tielens, A. Castets, E. Caux, Bertrand Lefloch, S. Maret. 2006

136 citations recorded by the source corpus.

Context. Despite the low cosmic abundance of deuterium (D/H ∼ 10 −5 ), high degrees of deuterium fractionation in molecules are observed in star-forming regions with enhancements that can reach 13 orders of magnitude, a level that current models have difficulty accounting for. Aims. Multi-isotopologue observations are a very powerful constraint for chemical models. The aim of our observations is to understand the processes that form the observed high abundances of methanol and formaldehyde in low-mass protostellar envelopes (gas-phase processes? chemistry on the grain surfaces?), as well as to better constrain the chemical models. Methods. With the IRAM 30 m single-dish telescope, we observed deuterated formaldehyde (HDCO and D2CO) and methanol (CH2DOH, CH3OD, and CHD2OH) towards a sample of seven low-mass class 0 protostars. Using population diagrams, we then derived the fractionation ratios of these species (abundance ratio between the deuterated molecule and its main isotopologue) and compared them to the predictions of grain chemistry models. Results. These protostars show a similar level of deuteration as in IRAS 16293−2422, where doubly-deuterated methanol – and even triply-deuterated methanol – were first detected. Our observations point to the formation of methanol on the grain surfaces, while formaldehyde formation cannot be fully pinned down. While none of the scenarii can be excluded (gas-phase or grain chemistry formation), they both seem to require abstraction reactions to reproduce the observed fractionations.

Subfields: Astronomy and Astrophysics, Organic Chemistry, Physical and Theoretical Chemistry

View Paper: https://www.semanticscholar.org/paper/be73dbc33a2dbb112e54e4ec89d7c66534b796d8

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Citations in the corpus

Exploring Molecular Complexity with ALMA (EMoCA): Deuterated complex organic molecules in Sagittarius B2(N2) (2015, methodology): “This would be nearly one order of magnitude lower than toward the Compact Ridge in Orion KL (0.5%, Neill et al. 2013) and about 50 times lower than toward Class 0 protostars (1.6%–4.7%, Parise et al. 2006).”
Our astrochemical heritage (2012, background): “References: H2O: [272], [113], [412], [73], [432]; H2S: [433]; NH3: [273],[426]; H2CS: [282]; H2CO: [92]; [342]; CH3OH: [343],[340], [342].”
The Molecular Universe (2011, background): “The observed high abundance of deuterated species (e.g., HDCO, D2CO, CH2DOH, CHD2OH, CD3OH, CH3OD, and NH2D; Parise et al. (2006); Ceccarelli et al. (2001)) is also taken as evidence for the importance of ice sublimation in these regions as high deuteration is characteristic for regions of ∼ 10 K, e”