Observed Ju = 3 and 4 (K_a = 0) transitions of the isomers of HCNS. The bottom panel shows the hyperfine components of the J = 5/2 − 3/2 transition of NCS in its ²Π_3/2 ground state. The abscissa corresponds to the rest frequency. The ordinate is the antenna temperature corrected for atmospheric and telescope losses, in mK. Blanked channels correspond to negative features produced when folding the frequency-switched data. The red line shows the computed synthetic spectra for these lines (see Sect. 3). The derived line parameters are given in Table A.1.