Observed hyperfine components of the N_J = 2₃−1₂ (upper panels) and N_J = 3₄–2₃ (bottom panels) transitions of CC³³S towards TMC-1. The derived line parameters of the observed lines are given in Table B.1. The abscissa corresponds to the rest frequency in MHz. The ordinate corresponds to the antenna temperature corrected for atmospheric and telescope losses in mK. The synthetic spectra (red line) are derived from the LVG model described in Section 3 with n(H₂)=1.3×10⁴ cm⁻³ and N(CC³³S)=3.5×10¹¹ cm⁻² (see Section 4.3).