PRESSURE AND TEMPERATURE EFFECTS ON MOLECULAR INTERACTIONS PROBED BY LIGHT SCATTERING AND FTIR (FERMI RESONANCE, SOL-GELS, INFRARED)

As molecules in any system move around, they will interact with their neighbors. The strength of this interaction depends on the mechanism and will be influenced by changing pressure and temperature. The former will change intermolecular spacing while the latter alters the kinetic energy. By controlling these, the relative strengths and weaknesses of different interactions within a single system may be probed using vibrational spectroscopy. This thesis will utilize three spectroscopic techniques to probe the effects of high pressure and varied temperature on several differing systems and physical phenomena.; The Raman spectra of ammonia and methanol are profoundly affected by Fermi resonance. This phenomenon will be in turn perturbed by the thermodynamic state for both systems. A quantitative analysis is performed on the coupled peaks of ammonia ((nu)(,1) and 2(nu)(,4)) and methanol ((nu)(,3) and 2(nu)(,4)) using two models, the Herzberg perturbations treatment and the coupled oscillator theory. The various parameters for ammonia are found to be influenced heavily by changes in the hydrogen bonding characteristics while those for methanol appear to depend more on repulsive interactions.; Raman scattering is also used to probe the dynamics of gelation in a sol-gel system. The breakdown (hydrolysis) of the starting reagent, tetramethyl orthosilicate, and the growth of the Si-O-Si network (condensation) are found to be altered by the presence of formamide, a drying control chemical additive. The time evolution spectra for sols with and without formamide are used to follow the reactions from the initial mixing to well beyond gelation.; Information regarding the low energy spectrum of sulfur hexafluoride is derived from a depolarized Rayleigh scattering experiment. An absolute intensity calibration is carried out first, using a new high pressure cell designed for this work. Comparison with previous experimental and theoretical results is carried out to determine the density effects on the spectra as well as the contributions from collisional, rotational and cross terms. This is done using the zeroth and second order moments.; Finally, an introduction to the FT-IR supercritical fluid solubility experiment is given. The specially designed high pressure cell and the FT-IR instrument are briefly described and some initial data discussed.