Critical Raman line shape behavior of fluid nitrogen
M. Musso, F. Matthai, D. Keutel, and K.-L. Oehme
Institut für Physik und Biophysik, Universität
Salzburg, Hellbrunnerstrasse 34,
A-5020 Salzburg, Austria
Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Strasse
1, D-85741 Garching, Germany
Carl Zeiss Jena GmbH, D-07745 Jena, Germany
Institut für Physikalische Chemie, Friedrich-Schiller-Universität
Jena, Helmholtzweg 4, D-07743 Jena, Germany
Abstract:
Isotropic Raman line shapes of simple molecular fluids exhibit critical
line broadening near their respective liquid-gas critical points. In
order to observe this phenomenon, it is essential that the band position
of a given vibrational mode is density-dependent, and that vibrational
depopulation processes negligibly contribute to line broadening. Special
attention was given to the fact that the isotropic (i.e., nonrotationally
broadened) line shape of liquid N2 is affected by resonant
intermolecular vibrational interactions between identical oscillators.
By means of the well-chosen isotopic mixture (14N2).975
- (14N15N).025, the temperature and
density dependences of shift, width, and asymmetry of the resonantly
coupled 14N2 and, depending on the S/N ratio available,
of the resonantly uncoupled 14N15N were determined, with
up to milli-Kelvin resolution, in the coexisting liquid and gas phases
and along the critical isochore, using a highest-resolution double monochromator
and modern charge-coupled device detection techniques. Clear evidence
was found that vibrational resonance couplings are present in all dense
phases studied.
*Lecture presented at the European Molecular Liquids
Group (EMLG) Annual Meeting on the Physical Chemistry of Liquids: Novel
Approaches to the Structure, Dynamics of Liquids: Experiments, Theories,
and Simulation,Rhodes, Greece, 7-15 September 2002. Other presentations
are published in this issue, pp. 1-261.
