LevelPopulation ratio (N_low∕N_up) at formation heights for transitions 2780.6 Å (left) and 71 097 Å (right), following the examples in Figs. 14a and b and Figs. 14c and d, respectively. Left panel: the ratios are identical for models 1401b (purple dashed-dotted line) and 1401c (red dashed-double-dotted line), producing the same line (shown in Fig. 9). Right panel: as in almost every IR transition, level population ratios are higher in model 1401b, producing deeper spectral lines (the line for this example is shown in Fig. 11d).