Molecular rotational spectra formulae

Absorption coefficients in terms of Einstein coefficients. Absorption coefficient per unit volumn of molecular gas is . From here on, the subscript “ul” of frequency has been omitted for clarity. Substituting Aul into this formula, one gets . Boltzmann distribution. In local thermal equilibrium (LTE), the molecular energy level population distribution nj obeys the Boltzmann distribution ... ................
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