Rotational diagrams for CH₃OH (upper panel), and CH₃CHO (lower panel) derived using the emission lines observed towards B1b (see Table 1 and Fig. 3). The parameters N_u, g_u, and E_up are the column density, the degeneracy, and the energy (with respect to the ground state of each symmetry), respectively, of the upperlevel. The derived values of the rotational temperature are reported in the panels.