Infrared Emissivities and Absorptivities of Gases

Approximate analytic expressions are obtained for the ``effective band widths'' and emissivities of diatomic molecules at elevated pressures. The absorptivities of molecular vibration-rotation bands are evaluated for radiation emitted by similar molecular vibration-rotation bands and for radiation emitted by blackbodies. The results obtained for the absorptivity calculations compare favorably with available empirical correlations for H2O. The postulated model does not apply to CO2 and, therefore, no satisfactory theoretical formula has been derived for the absorptivities of this molecule. The appendix (by A. Thomson) is devoted to a critical examination of the limits of validity of the effective band-width concept for different molecules.