Anomalous behaviour in the vibrational Raman spectra of N₂, O₂, and CO under near critical conditions

Ali, Naushad (1978) Anomalous behaviour in the vibrational Raman spectra of N₂, O₂, and CO under near critical conditions. Masters thesis, Memorial University of Newfoundland.

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    Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission.
    (Original Version)

Abstract

Experimental studies of the isothermal density dependence of frequency shift and line-width of the Raman Q-branches of N₂, O₂ and CO gases have been done. Light (514.5nm Wavelength) from an Ar-ion laser was focused at the centre of a temperature controlled cell containing the sample, and scattering at 90° was analyzed and recorded by photon counting techniques using a piezoelectrically scanned Fabry-Perot interferometer, photo-multiplier tube and a data acq1uisition and stabilization system. -- The isothermal Raman frequency shift and line-width (FWHM) data were collected over a density range of 10 Amagat to 450 Amagat (70 psi - 1000 psi) for a set of temperatures close to the critical temperature (Tc) for each gas (N₂, O₂ & CO). It was found that the density dependences of both the shift and width exhibited anomalous behavior under near-critical conditions. The anomaly reduced for temperatures away from the critical temperature, and was found to vanish completely in the case of frequency shift at T-Tc ≥ 3K. -- The observed effects are qualitatively interpreted in terms of ‘local density’ fluctuations associated with molecular cluster formation. It is assumed that cluster condensation occurs at a particular value of density ρcc, characterized by a large and sudden change in the mean cluster life-time. It is interpreted that for densities ρ < ρcc, the observed Raman spectrum is mainly due to unclustered molecules and for densities ρ > ρcc, the observed Raman spectrum is dominantly due to molecular clusters. Finally, it is concluded that the Raman effect could be of great importance as a probe of density fluctuations in the critical region.

Item Type: Thesis (Masters)
URI: http://research.library.mun.ca/id/eprint/7592
Item ID: 7592
Additional Information: Bibliography: leaves 96-98.
Department(s): Science, Faculty of > Physics and Physical Oceanography
Date: 1978
Date Type: Submission
Library of Congress Subject Heading: Gases--Spectra; Raman spectroscopy

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