Methods for calculating the emission characteristics of a molecular gas in vibrational–rotational transitions involving information collected in the HITRAN database have been discussed. It has been shown that a series of vibrational–rotational transitions induced by the absorption of photons by CO2 molecules lead to the formation of unstable autoionizing states. Algorithms for calculating the partial absorption coefficients and radiation fluxes from the bulk of the molecular gas have been developed involving the HITRAN database. Advantages and disadvantages of this approach for calculating the emission characteristics of molecular gas layers have been discussed. The results have been demonstrated in application to carbon dioxide and methane in the Earth’s atmosphere.