Knowledge Bank

The formation of the metastable isomer pair, HNCS and HSCN, has been investigated in the warm molecular cloud SgrB2 and the dense cold core TMC-1. In Sagitarius B2, the $8\_0\_,\_8$--$7\_0\_,\_7$ and $9\_0\_,\_9$--$8\_0\_,\_8$ transitions of both isomers have been mapped over a $5\ast 3$ region around the central hot core SgrB2(M), using the Arizona Radio Observatory (ARO) 12m telescope. In TMC-1, the $8\_0\_,\_8$--$7\_0\_,\_7$ and $7\_0\_,\_7$--$6\_0\_,\_6$ lines of both isomers have been detected. Both molecules show extended emission across SgrB2 with a ratio [HNCS]/[HSCN] $1-10$. In TMC-1, the ratio is $1$. The high abundance of the metastable isomer HSCN relative to HNCS suggests that the main production route to both molecules is electron recombination from the ionic precursor HNCSH+, in analogy to HCN and HNC.