Population diagrams of HNCO, HNCS, HC₃N, and NO (from top to bottom) and best linear fit (dashed line) to the data points (filled symbols; from Table 3). In the case of HNCO, black squares represent transitions with K_a = 0 and grey triangles the K_a = 1 transitions. The values of T_rot and N_tot derived from the fit are indicated in the bottom left corner of each box. An opacity correction is not applied in these cases because all the transitions are optically thin. Error bars as in Fig. 8.