Raman investigation of vibrational energy interactions during nanoscale confinement

The Raman scattering parameters of linewidth and peak energy of liquids that are undergoing local nanoscale spatial confinement are investigated. This is done using several polar and nonpolar liquid molecules of varying size, weight, shape, and polarity that are placed inside different nanometer-sized silica glass pores. Nanoscale confinement is shown to produce changes in the Raman spectra that are related to different quantum effects. Raman spectra are collected from filled porous glass samples with average pore sizes of 2.5, 5, 10, and 20 nm. The resulting spectra are then compared to bulk liquid samples. The most salient spectral changes of individual vibrational modes, overtone modes, and combinations modes of methanol, deuterated methanol, acetone, benzene, carbon disulfide, carbon tetrachloride, and beta-carotene are graphed and tabularized. Results illustrate how different types of molecular vibrations respond to confinement, and how molecular geometrical restrictions affect Raman active modes based on the ratio of pore size to molecular size. Nano-confinement allows for the direct measurement of how intra-molecular and inter-molecular forces affect the expression of vibrational resonant peak energies as well as vibrational dephasing times. The outcome demonstrates a preference for polar molecules, specific vibrational types, and ratios of molecular size to cavity size.