Raman Spectroscopy of Dense Fluids. Temperature and Pressure Effects on Vibrational Relaxation, Molecular Reorientation and Spectral Frequencies
Sharko, Paul Theodore
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Permalink
https://hdl.handle.net/2142/67225
Description
Title
Raman Spectroscopy of Dense Fluids. Temperature and Pressure Effects on Vibrational Relaxation, Molecular Reorientation and Spectral Frequencies
Author(s)
Sharko, Paul Theodore
Issue Date
1980
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Physical
Language
eng
Abstract
This work reports measurements of the Raman spectra of the Si-CH(,3) and C-H stretching modes of tetramethylsilane, the C-H stretching mode of fluoroform, and the C = O stretching mode of acetone. All spectra were measured under independently varied conditions of temperature and pressure.
The isotropic spectra of tetramethylsilane were measured at temperatures from 0(DEGREES) to 100(DEGREES)C and at pressures up to 4000 bar. It was found that the spectral widths of the Si-CH(,3) stretching mode are determined by a dephasing mechanism of vibrational relaxation but the widths of the C-H stretching mode are determined by inhomogeneous vibrational broadening. The pressure and temperature dependence of vibrational frequency are also tabulated and are found to follow a trend similar to that seen in other molecules.
Both polarized and depolarized spectra of fluoroform were taken from 0(DEGREES) to 100(DEGREES)C and at pressures up to 2000 bar. The pressure and temperature dependence of the isotropic spectral widths were found to agree well with the predictions of the vibrational dephasing mechanism. The Fermi resonance contribution to the line width was evaluated and found to be small with respect to the experimental line width. Anisotropic spectral widths were compared to previous measurements and to the Debye equation. It was also found that there is a pressure-dependent displacement between polarized and depolarized spectra which ranges up to 5 cm('-1).
The polarized and depolarized spectra of acetone were measured at temperatures from -25(DEGREES) to 50(DEGREES)C and at pressures up to 4000 bar. The isotropic spectral widths were found to decrease as pressure is increased, contrary to the trend observed in other molecules. This behavior is attributed to effects of dipole-dipole interaction. As was also seen in fluoroform, there is a pressure dependent frequency displacement between polarized and depolarized spectra. The depolarized spectra are observed at higher frequencies. This effect is also attributed to dipole interactions.
Measurements of the C-CH(,3) stretching mode in neopentane and the N-O stretching mode in molten sodium nitrate are also reported. Additionally, a procedure for measuring pressure-induced birefringent effects in pressure cell windows is proposed.
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