The Infrared Pleochroism of Lawsonite: The Orientation of the Water and Hydroxide Groups

Polarized infrared absorption spectra of thin single crystals of lawsonite, CaAI_2(OH)_2Si_2O_7H_2O_2, have been measured at room temperature and near 78 K. These data suggest a structural model in which the hydrogen atoms of both OH and H_2O lie in planes parallel to (001). The polanzat1on data demand that the order of the energies of the symmetric and antisymmetric stretch of the crystallographically ordered water in lawsonite be reversed from that of liquid water