Raman spectroscopic studies on structure I and structure IItrimethylene oxide hydrate

Abstract

Raman spectra were collected from structure I (sI) and structure II (sII) trimethylene oxide (TMO) hydrates at various temperatures and used to assign the vibrational modes, investigate the ordering of TMO molecules inside the cage structure, and to determine possible interactions between the guest and the host lattice. Only Raman spectra from sI hydrate could be analyzed since the low concentration of TMO prevented sII peaks from being resolved. Comparison of the Raman spectra of liquid, solid, and enclathrated TMO (sI) showed Raman shifts to higher wave numbers for the enclathrated TMO; mainly among the ring modes. The ring and (or) skeletal modes around 930 cm–1 and the asymmetric CH2 stretching mode around 2970 cm–1, showed shifts greater than 10 cm–1. These observed changes are interpreted on the basis of the "loose-cage – tight-cage" model, which interprets the shift as arising from strain induced by the hydrate cage on the guest TMO molecules in the 62 cages. In addition, variable temperature Raman studies, in the temperatures ranging from 103 to 203 K, showed no evidence of ordering and (or) reorientation of host molecules. PACS No.: 78.30.-j