A simple empirical model for the collisional spectral shift of air-broadened CO₂ lines

A simple empirical model is proposed for the pressure-induced shifts of air-broadened CO₂ absorption lines. It is based on the introduction of components symmetric and antisymmetric with respect to the rotational quantum number m, and on a separation of vibrational and rotational contributions. These components are modelled though empirical analytical laws with parameters that are obtained from fits of the measured shifts in only two different bands. It is then shown that the model leads to satisfactory results for a number of other vibrational transitions in which the shifts take significantly different values. This provides a simple way to generate values for unmeasured transitions and this tool can thus be used to complement spectroscopic databases.