Single- and multi-photon absorption of carbon dioxide laser lines by SO₂ and CO₂ molecules

We have used 60 rovibrational lines of a Lumonics TEA CO₂ laser to record the spectra of coincidence of SO₂ IR absorption with CO₂ laser emission. We extended the same type of investigation to CO₂ molecules and observed an absorption at practically all the rovibrational lines of the laser. We have also recorded the increase of absorption with pressure of the studied molecule and with its temperature. Our work reveals very accurately the fine structure of these absorptions that shows a clear discreteness in the intensities of the lines. Some implication of this discreteness in multiphoton absorption is also presented, through data that indicate very strong vibrational coupling between ground and excited electronic states of SO₂.