Laboratory measurements of the three hyperfine components of the N_J=2₁−1₀ rotational transition of CC³³S we observed. The abscissa corresponds to the frequency of the lines in MHz. The spectra were achieved by 100-shots of accumulation. The coaxial arrangement of the adiabatic expansion and the resonator axis in the FTMW spectrometer produces an instrumental Doppler doubling. The resonance frequencies are calculated as the average of the two Doppler components.