Raman microprobe polarization measurements as a tool for studying the structure and orientation of molecules and clusters incorporated into cubic zeolites: S8 and Se12 rings in zeolite A

Abstract

Raman spectra of molecules or clusters incorporated into cubic zeolites are usually studied using microcrystalline powder samples, light being completely unpolarized because of multiple reflection on microcrystal surfaces. Therefore, all information about symmetry of the Raman-active vibrations of species and orientation of species in zeolite cavities is lost. In order to save this information, we propose to do Raman microprobe polarization measurements of cubic zeolite single crystals containing examined species. We theoretically consider examples of high-symmetry anisotropic species (planelike or rodlike molecules or clusters with the threefold or higher major axes) incorporated into cubic zeolite A. We experimentally study polarization and angular dependencies of Raman spectra of S8 and Se12 rings incorporated into zeolite A single crystal. The obtained dependencies correspond to the C4v point group symmetry S8 rings oriented by their fourfold axes along the fourfold axes of zeolite and the D3d point group symmetry Se12 rings oriented by their threefold axes along the threefold axes of zeolite. The method applied to the S8 and Se12 rings is considered as a new powerful tool for studying the structure and orientation of a wide class of cubic-zeolite-confined species.