2018ApJS..236...45G

We present molecular line observations of the high-mass molecular clump IRAS 16562-3959 taken at 3 mm using the Atacama Large Millimeter/submillimeter Array at 1.''7 angular resolution (0.014 pc spatial resolution). This clump hosts the actively accreting high-mass young stellar object (HMYSO) G345.4938+01.4677, which is associated with a hypercompact H II region. We identify and analyze emission lines from 22 molecular species (encompassing 34 isomers) and classify them into two groups, depending on their spatial distribution within the clump. One of these groups gathers shock tracers (e.g., SiO, SO, HNCO) and species formed in dust grains like methanol (CH₃OH), ethenone or ketene (H₂CCO), and acetaldehyde (CH₃CHO). The second group collects species closely resembling the dust continuum emission morphology and are formed mainly in the gas phase, like hydrocarbons (CCH, c-C₃H₂, CH₃CCH), cyanopolyynes (HC₃N and HC₅N), and cyanides (HCN and CH₃C₃N). Emission from complex organic molecules (COMs) like CH₃OH, propanenitrile (CH₃CH₂CN), and methoxymethane (CH₃OCH₃) arise from gas in the vicinity of a hot molecular core (T >= 100 K) associated with the HMYSO. Other COMs such as propyne (CH₃CCH), acrylonitrile (CH₂CHCN), and acetaldehyde seem to better trace warm (T <= 80 K) dense gas. In addition, deuterated ammonia (NH₂D) is detected mostly in the outskirts of IRAS 16562-3959 and associated with near-infrared dark globules, probably gaseous remnants of the clump's prestellar phase. The spatial distribution of molecules in IRAS 16562-3959 supports the view that in protostellar clumps, chemical tracers associated with different evolutionary stages-starless to hot cores/H II regions-exist coevally.