| In this thesis, fifth-order nonresonant Raman spectroscopy is used to study the intermolecular motions of carbon disulfide so as to address fundamental questions about liquid dynamics. These questions, such as how diffusive dynamics (i.e. those involving structural change) emerge from fluctuations of individual molecules around their equilibrium positions, are directly addressed by fifth-order nonresonant Raman spectroscopy. This is due to the fifth-order signal's sensitivity to (and dependence upon) electrical or mechanical anharmonicity of the studied system, which is not a characteristic of lower-order spectroscopies. In this thesis, first it is shown that early attempts to measure the fifth-order nonresonant Raman signal of the low frequency motions of liquids were marred by the presence of lower-order cascading signals. These cascading signals do not depend on anharmonicity and thus do not contain the detailed molecular information that the fifth-order signal contains. It is shown that careful consideration of phase matching conditions allows one to suppress the lower-order cascading processes in favor of the desired fifth-order signal. In order to understand the measured fifth-order signals, both comparison to theory and signal processing is employed. An analysis of the full polarization dependence of the signal, based on early instantaneous normal mode analysis, is presented. A Fourier deconvolution of the measured signal is performed in order to isolate the portion of the fifth-order response most directly related to the details of liquid motion. Next, a heterodyne detection scheme, which allows for measurement of the sign and phase of the fifth-order nonresonant signal, is introduced. Heterodyne detected data from carbon disulfide is compared with simulations based on various theories. Most fruitfully, the data is compared with molecular dynamics simulations. Such comparison allows pinpointing the origin of key features of the measured signals. |
