Determination of the rotational relaxation cross section of carbon dioxide from spectral measurements

The pressure-induced transformation of the spectrum of the Q branch of the ν₁ mode (1388 cm^?1) of CO₂ molecules is quantitatively interpreted. The contributions to the width of the spectrum from three relaxation mechanisms—vibrational dephasing, rotational relaxation, and the Doppler effect—are taken into account. From the fitting of the calculated and measured spectra of the Q branch, the effective cross section of the rotational energy relaxation is determined.