Laboratory and astronomical discovery of cyanothioketene, NCCHCS, in the cold starless core TMC-1

We present the detection of cyanothioketene, NCCHCS, in the laboratory and toward TMC-1. This transient species was produced through a discharge of a gas mixture of CH$_2$CHCN and CS$_2$ using argon as carrier gas, and its rotational spectrum between 9 and 40 GHz was characterized using a Balle-Flygare narrowband-type Fourier-transform microwave spectrometer. A total of 21 rotational transitions were detected in the laboratory, all of them exhibiting hyperfine structure induced by the spin of the N nucleus. The spectrum for NCCHCS was predicted in the domain of our line surveys using the derived rotational and distortion constants. The detection in the cold starless core TMC-1 was based on the QUIJOTE$^1$ line survey performed with the Yebes 40m radio telescope. Twenty-three lines were detected with $K_a$=0, 1, and 2 and $J_u$=9 up to 14. The derived column density is (1.2pm 0.1)times 1011 cm$^ $ for a rotational temperature of 8.5pm 1\,K. The abundance ratio of thioketene and its cyano derivative, H$_2$CCS/NCCHCS, is 6.5pm 1.3. Although ketene is more abundant than thioketene by sim 15 times, its cyano derivative NCCHCO surprisingly is not detected with a 3sigma upper level to the column density of 3.0times 1010 $, which results in an abundance ratio H$_2$CCO/NCCHCO \,$>$\,430. Hence, the chemistry of CN derivatives seems to be more favored for S-bearing than for O-bearing molecules. We carried out chemical modeling calculations and found that the gas-phase neutral-neutral reactions CCN + H$_2$CS and CN + H$_2$CCS could be a source of NCCHCS in TMC-1.