Molecular hydrogen level population diagram relative to the H₂(1−0)S(1) transition. The column density N is given in [m^-2]. The center r = 1″ region marks the energy of the level, the other regions are shifted for a better presentation in the plot. The models are for dense UV-excited gas taken from Davies et al. (2003). The linear fit is to the v = 1 levels of region cPSF which yields a kinetic excitation temperature of T_exc ~ 1800 K.