Graduate Thesis Or Dissertation
 

Vibrational and reorientational lifetimes in liquids determined by Raman spectroscopy

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  • Studies of anisotropic and isotropic Raman line shape yield information about the rotational motion (rotational correlation function) and non-reorientational (vibrational) lifetimes. The rotational motion of carbon disulfide has been studied previously by the techniques of Raman spectroscopy (6, 43), Rayleigh scattering (43, 46) and direct measurement (47). This work was undertaken because the v₁ vibrational mode is low enough in energy so that several excited states are occupied, and because of anharmonicity the v₁ consists of numerous components. In addition, there are several isotopic components. These various components may complicate and invalidate previous calculations of correlation functions which neglect them. We analyzed the isotropic spectrum and found ten such components in the V₁ band and considered these in analyzing the anisotropic spectrum. Our results, which are not fully understood, indicate a nearly Lorentzian band shape for each component--i. e. , simple exponential decay of the correlation function--but with shorter time constants than previous literature values. The Raman spectra of the 2v₂ region, which is in Fermi resonance with v₁, and the Raman forbidden v₂ mode were also studied. These regions also indicate isotopic and hot band contributions. Standard expressions of polarization ratios, which are required to be known accurately for correct correlation function calculations, are given for strict 90° scattering in the limit of vanishing collection aperture. The effects of finite collection aperture were investigated, compared to existing literature and studied experimentally for the v₁ mode of CCl₄. The experimental verification of the predicted finite aperture effects was inconclusive, presumably due to an inadequate knowledge of the behavior of the polaroid analyzer to oblique radiation and a non-point scattering source.
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