Panels a), b). Population diagram of CHCN, ν= 0 toward Sgr B2(N2). Only the lines that are clearly detected and do not suffer too much from contamination from other species are shown. The observed data points are shown in black while the synthetic populations are shown in red. No correction is applied in panel a). In panel b), the optical depth correction was applied to both the observed and synthetic populations and the contamination from all other species included in the full model was removed from the observed data points. The purple line indicates a linear fit to the observed populations (in linear-logarithmic space). The derived rotation temperature is given in Table 7. Panels c), d): same as panels a), b) for CN, ν= 0. Panels e), f): same as panels a), b) for CN, ν= 0.