Dynamics of confined methyl iodide studied by Raman spectroscopy

Raman spectroscopy was used to study the vibrational and reorientational dynamics of bulk and confined liquid methyl iodide. A set of five porous silica glasses with pore radii ranging from 15 to 38 Å was employed as the confining material. With decreasing pore size a decrease in the ν3 (C– I) vibrational correlation time and an increase in the molecular reorientational correlation time were found. It is noted that the two-state fast-exchange model is not applicable in Raman studies owing to slow diffusion of pore molecules compared with the Raman spectroscopic time-scale. A phenomenological linear correlation between the correlation times and the reciprocal of the pore radius was found to be useful and employed for data analysis. A relatively low sensitivity of the reorientational dynamics of methyl iodide to confinement was explained by considering the shape and mass distribution of a methyl iodide molecule.