The ALMA-PILS survey: First detections of deuterated formamide and deuterated isocyanic acid in the interstellar medium

Abstract

Formamide (NH 2 CHO) has previously been detected in several star-forming regions and is thought to be a precursor for different prebiotic molecules. Its formation mechanism is still debated, however. Observations of formamide, related species, and their isopotologues may provide useful clues to the chemical pathways leading to their formation. The Protostellar Interferometric Line Survey (PILS) represents an unbiased, high angular resolution and sensitivity spectral survey of the low-mass protostellar binary IRAS 16293-2422 with the Atacama Large Millimeter/submillimeter Array (ALMA). For the first time, we detect the three singly deuterated forms of NH 2 CHO (NH 2 CDO, cis-and trans-NHDCHO), as well as DNCO towards the component B of this binary source. The images reveal that the different isotopologues are all present in the same region. Based on observations of the 13 C isotopologues of formamide and a standard 12 C/ 13 C ratio, the deuterium fractionation is found to be similar for the three different forms with a value of about 2%. The DNCO/HNCO ratio is also comparable to the D/H ratio of formamide (∼1%). These results are in agreement with the hypothesis that NH 2 CHO and HNCO are chemically related through grain-surface formation.

Interstellar Formamide (NH2CHO), a Key Prebiotic Precursor

“…Also, Skouteris et al characterized the isotopic effect when considering partially deuterated reactants in an attempt to simulate the D-enrichment of formamide in the protostar IRAS 16293-2422 as it resulted from an ALMA detection campaign. 17 Also in this case, the excellent agreement between the observed and predicted values is in favour of a gas-phase origin of formamide, as also discussed in Sect. .…”

“…Figure 1 shows a plot of NH 2 CHO against HNCO fractional abundances relative to molecular hydrogen, H 2 , for all the sources in the literature with reported values of column densities for these two molecules, as well as total H 2 column density values. 17,28,29,42,43,[45][46][47]62,64,72,73 Single-dish and interferometric ob- Figure 1 shows that there is a tight correlation between the two molecular species, which is almost linear and holds across several orders of magnitude in molecular abundance. This has led some authors to propose that HNCO and NH 2 CHO are chemically linked, with either both of them forming from a common precursor, or one forming from the other.…”

Chemical segregation in hot cores with disk candidates

“…The striking physical connection between these two species makes a strong case for the formation of formamide predominantly through the hydrogenation of HNCO. Coutens et al (2016) has also recently observed co-spatial emission in HNCO and Formamide in the low mass protobinary system IRAS16293.…”

Exploring the formation pathways of formamide

“…This correlation between the abundances of these species is nearly linear, suggesting that the two molecules are chemically related. Atacama Large Millimeter/submillimeter Array (ALMA) observations by Coutens et al (2016) of IRAS 16293-2422 show that the deuterium fractions in HNCO and NH 2 CHO are very similar, implying a chemical link. On the other hand, Codella et al (2017) observed a shock near L1157-B1 using interferometric observations.…”