2017MNRAS.469.2230M

We report the detection of the pre-biotic molecule CH₃NCO in a solar-type protostar, IRAS16293-2422 B. A significant abundance of this species on the surface of the comet 67P/Churyumov-Gerasimenko has been proposed, and it has recently been detected in hot cores around high-mass protostars. We observed IRAS16293-2422 B with the Atacama Large Millimeter Array in the 90 to 265 GHz range, and detected eight unblended transitions of CH₃NCO. From our Local Thermodynamic Equilibrium analysis, we derived an excitation temperature of 110 ± 19 K and a column density of (4.0 ± 0.3) x 10¹⁵ cm^–2, which results in an abundance of <=(1.4 ± 0.1) x 10^–10 with respect to molecular hydrogen. This implies a CH₃NCO/HNCO and CH₃NCO/NH₂CHO column density ratios of ∼0.08. Our modelling of the chemistry of CH₃NCO suggests that both ice surface and gas phase formation reactions of this molecule are needed to explain the observations.