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The goal of the project was to research the method of spectroscopy which is best adapted to obtain very excited vibrational states in acetylene at energies where the classical movement of the molecule becomes chaotic.

The stimulated emission pumping (SEP) spectra technique presented some advantages but also serious limitations. It is a double resonance technique where a laser provides an initial intermediate excitational state which is then increased using a second laser stimulation. The intensity of the second laser is very important in this technique and can result in an overall reduction in fluorescence. Non linear effects of the technique also render interpretation of results difficult. Perhaps the greatest problem however, is that very long time periods are involved in obtaining high resolution spectra thereby rendering the technique inappropriate.

A second technique used, involving the use of stimulated photon echoes, also failed to provide satisfactory results. We then turned to an extremely simple technique known as dispersed fluorescence (DF). Using the advanced technologies we had developed through our previous laser system, as well as a better theoretical comprehension of the acetylene molecule, we have been able to choose an intermediate excited state to succeed in obtaining pure vibrational spectra.
A new spectroscopic technique is proposed to record the high-vibrational spectra of the electronic ground state of CS2. The measurement of tri-level photon echo intensity as a function of stimulating pulse frequency will provide improved signal-to-noise ratio over curently employed spectroscopic methods. Fourier transform techniques will be used to analyze the recorded spectra in order to reveal i)the onset of quantum chaos in this molecular system with the disappearance of good vibrational quantum numbers ii) the re-emergence of large amplitude vibrational modes within the chaotic region that may promote the onset of chemical reaction and iii) features identifiable with the results of computer models of molecular vibration.


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Université de Grenoble (Université Scientifique et Médicale)
EU contribution
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38402 Saint-Martin-d'Hères

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