Q-band (top panels) and W-band (bottom panels) observations of OCS at a total pressure of 0.04 mbar in the chamber. The frequency switching mode has been used with a throw of 37 MHz. The different panels for each band always show the same frequency range but with a different intensity scale. The observing time per W sub-band (WL, WM, and WH) is 2.2 h. Hence, the Q band has been observed for 6.6 h. The rotational transitions of the main isotopologue are indicated. Features corresponding to OC³⁴S and OC³³S are also indicated. A zoom-in on the J = 9 → 8 transition is shown in Fig. 12. The same transition, but in a narrower frequency range, of OC³⁴S, OC³³S, O¹³CS, O¹³C³⁴S, ¹⁷OCS, ¹⁸OCS, and OC³⁶S is shown in Fig. C.2. The different isotopologues of OCS are observed in natural abundance. The negative features seen in the different panels are produced by the folding of the frequency switched data and appear at ±37 MHz of each rotational transition. The data shown in this figure have been smoothed by a two-channel box procedure.