The spectral absorption coefficient, ?(?) m??, is an optical property that quantifies how strongly a material absorbs radiation at a given wavelength (or wavenumber). Knowledge of the CO? absorption coefficient is essential for modeling thermal radiative heat transfer in the atmosphere. In this work, we report ?(?) and its spectrally averaged value a for: (i) pure CO?, (ii) CO??air mixtures, and (iii) CO??argon mixtures. In the mixtures, the CO? concentration was doubled, quadrupled, and increased up to fifteen times relative to the presentday concentration in the atmosphere The spectral absorptivity A(?) was measured in a 1.8 m long test tube at normal temperature and pressure using a Nicolet FTIR spectrometer, with 0.5 cm-1 resolution. We focused on the 15 ?m band (wavenumbers 800 cm-1 to 600 cm-1) because is the only CO? band that can trap the heat emitted by Earth. The measured spectra show that doubling the CO? concentration from 420 ppm to 840 ppm increases the averaged absorption coefficient a by approximately 20 %. A drastic increase in ?(?) was observed when air molecules were added to pure CO?, due to Vibrational-Translational (V-T) de-excitation by collisions. A similar increase was demonstrated when Argon atoms were added to pure CO?.
Aleksandar Ostrogorsky (Thu,) studied this question.