Intracavity Raman experiment

Ethylene has no dipole moment and a center of symmetry and therefore the Raman spectrum is an important source of structural information. After the early work on the rotational (Dowling and Stoicheff, 1959) and rovibrational Raman spectrum (Feldman et ah, 1956) these spectra were thoroughly studied in a series of publications (Hills and Jones, 1975 Hills et ah, 1977 Foster et ah, 1977). Overtones and combination bands were measured in an intracavity Raman experiment by Knippers et ah (1985). The Q-branch of the U2 band was resolved by pulsed CARS spectroscopy in a molecular beam experiment (Byer et ah, 1981). 

Nevertheless, it is possible to give a formal description of a statistical-limit molecule in the same terms as previously used in the strong-coupling case. It is well known that the emission spectrum of large molecules (studied up to now only in condensed phases) is composed of narrow bands (considered as the resonance Raman scattering) and broad-band fluorescence. The relative intensity of the first component is enhanced in presence of fluorescence quenchers (Friedman and Hochstrasser, 1975), or in laser intracavity experiments (Bobovich and Bortkevich, 1977). The first component may be related to the emission from nonstationary s> states with redistribution time shorter than the exciting-pulse duration. The second component would be due to the rapid vibrational redistribution. In the limiting case of nonfluorescent molecules only the resonance Raman spectrum persists. The nonradiative deactivation of the excited state would be more rapid here than the vibrational redistribution. 

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