Non-LTE spectral absorption coefficients for electronic band systems of diatomic molecules

Analytical expressions have been derived for the average non-LTE spectral absorption coefficients and the associated spontaneous spectral emission coefficients for electronic bands of anharmonic oscillators. Relatively simple differential expressions are provided for the important practical conditions under which the smeared-rotational-line approximation is applicable and for which individual rotational temperatures exist for the populations in each pair of the vibrational levels of interest. Further simplifications are given for the cases in which also vibrational temperatures exist for the populations of the two electronic states considered and in which the displacement of the band-heads from the band-centers can be neglected.