Sulphur-Bearing and Complex Organic Molecules in an Infrared Cold Core
  Since the start of ALMA observatory operation, new and important chemistry of
infrared cold core was revealed. Molecular transitions at millimeter range are
being used to identify and to characterize these sources. We have investigated
the 231 GHz ALMA archive observations of the infrared dark cloud region C9,
focusing on the brighter source that we called as IRDC-C9 Main. We report the
existence of two sub-structures on the continuum map of this source: a compact
bright spot with high chemistry diversity that we labelled as core, and a
weaker and extended one, that we labelled as tail. In the core, we have
identified lines of the molecules OCS(19-18), $^{13}$CS(5-4) and
CH$_{3}$CH$_{2}$CN, several lines of CH$_{3}$CHO and the k-ladder emission of
$^{13}$CH$_{3}$CN.We report two different temperature regions: while the
rotation diagram of CH$_{3}$CHO indicates a temperature of 25 K, the rotation
diagram of $^{13}$CH$_{3}$CN indicates a warmer phase at temperature of
$\sim450$K. In the tail, only the OCS(19-18) and $^{13}$CS(5-4) lines were
detected. We used the $Nautilus$ and the \textsc{Radex} codes to estimate the
column densities and the abundances. The existence of hot gas in the core of
IRDC-C9 Main suggests the presence of a protostar, which is not present in the
tail.
