September 2023
Thiocyanato radical

As reported in Astronomy & Astrophysics in 2021, the thiocyanato radical (NCS) was discovered by Cernicharo and co-workers toward TMC-1 using the Yebes 40m and IRAM 30m telescopes. Only one rotational transition was observed, but its hyperfine lines were resolved. The detection was based on prior experimental studies of the rotational spectrum of the radical, by Amano & Amano, Maeda, Habara, & Amano, and McCarthy et al. Four other sulfur-containing molecules were discovered in the same study: HCCS, H2CCCS, C4S, and thioketene, H2CCS.

Researcher Links
J Cernicho
C Cabezas
M Agúndez
B Tercero
JR Pardo
N Marcelino
JD Gallego
F Tercero
JA López-Pérez
P de Vicente

The thiocyanonato radical is the kajillionth detected cyano compound. NCS is the sulfur analog of the isocyanato radical, NCO, which has evidently not yet been detected in space. NCS is sometimes identified as thiocyanogen, but that term is generally reserved for the dimer, (NCS)2 or N≡C–S–S–C≡N (which has a non-planar structure analogous to hydrogen peroxide).

While the thiocyanato radical is often depicted (as in the animation above) possessing a triple bond between carbon and nitrogen and a single bond between carbon and sulfur, there is another resonance form in which there are double bonds between both pairs of atoms (as shown below). This means that there is radical character on both of the terminal atoms. A hydrogen atom can be added on either end to form two known astromolecules HSCN and HNCS.

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