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.
Collision-induced absorption (CIA) by CO2 is measured in the 1100–1600 cm−1range using a Fourier-transform spectrometer with a resolution of 0.5 cm−1. The current measurements, which agree well with previous ones but are more precise, reveal pronounced structures on top of both unresolved Fermi doublet bands consisting of P-, Q-,and R-like branches. Assignment of Q-branches at 1284.75 cm−1and 1387.75 cm−1to (CO2)2 dimers seems highly probable. The nature of other peaks observed in CIA and Raman spectra of the CO2 Fermi doublet region is discussed.
