Absorption spectra of pure CO2 have been recorded in the vicinity of the 2675 cm−1 Fermi triad for temperatures between 211 K and 296 K. The 2ν1, ν1 + 2ν2, 2ν2 collision-induced components have been extracted from the measured spectra, including for the low frequency band at 2547 cm−1, which is strongly masked by the ν3 wing absorption. Dimeric features are clearly seen on top of the structureless profiles. Integrated intensities of the Fermi-triad components are determined as a function of temperature.
The ν1 band of gaseous carbon dioxide has been studied in pressure-induced absorption at temperatures of ~ 190, ~ 300, and ~ 470 K, over a density range from 0.5 to 300 amagat, and with path lengths from 0.007 to 56 m. The observed temperature variation of the binary absorption coefficient can be satisfactorily accounted for only by adding a quadrupole–quadrupole interaction term to the usual Lennard–Jones model for the inter-molecular potential. The band profile is in agreement with the theory of quadrupole-induced absorption. There is some increase in the intensity of the band near the critical point due to the divergence of the correlation length. A very marked increase in the intensity is possibly prevented by the "cancellation effect".
