Knowledge Bank

The CARS spectra of natural $CO2$ have been recorded over the entire $2V2$ and 2 $V2$ spectral region with a resolution of $0.07cm-1$ for different temperatures: 300, 800, 1200 and 1500 K. As a first step, we have studied carefully the spectra at 300 and 800 K. Eleven different bands have been identified in the room temperature spectra whereas 46 vibrational bands appear in the spectrum at 800 K. We have not only assigned the Q branches but also many O and S rotational lines mainly for the first hot bands. A theoretical calculation of the CARS intensities has been performed. For this purpose, the $CO2$ wave functions have been calculated taking into account the Fermi resonance as well as the $\ell$-type doubling and the Coriolis interaction. In addition, for the simulation of the Q branches, a simple theoretical model describing the motional narrowing phenomenon has been used. Under these conditions, it has been possible to compute theoretical spectra which are in excellent agreement with the experimental ones. Moreover, new experimental values have been determined for the centers of five bands originating from highly excited states of $CO2$. Finally, in the spectra at 1200 and 1500 K, we have identified several hot bands which had never been observed before.""