title: Isosbestic-like point in the polarized reflectance spectra of monoclinic crystals--A quantitative approach.
abstract: If two overlapping bands originate from transition moments that are perpendicular and lie along the principal axes of the infinity frequency dielectric tensor, an isosbestic-like point (ILP) appears in the overlaid polarized IR reflectance spectra of single crystals. These conditions can also be met in principle in case of the reflectance from the ac-plane of a monoclinic crystal despite of the crystal's low symmetry. In order to determine the transition moment directions, diagonalization of the infinity frequency dielectric tensor should be performed. It is shown that a critical magnitude for the appearance of ILP is the angle of incidence. An increase of this angle leads to a transformation of the ILP to an isosbestic-like region, which eventually vanishes at higher incidence angles. Polarized reflectance spectra of gypsum (CaSO4.2H2O), recorded from the ac crystal face, were used to verify the theoretical results.
authors.affiliation: Institute of Chemistry, Faculty of Natural Sciences and Mathematics, Sts Cyril and Methodius University, Arhimedova 5, 1000, Skopje, Macedonia. vladimir@iunona.pmf.ukim.edu.mk
authors.forename: Vladimir
authors.initials: V
authors.lastname: Ivanovski
authors.forename: Thomas G
authors.initials: TG
authors.lastname: Mayerhöfer
authors.forename: Jürgen
authors.initials: J
authors.lastname: Popp
mesh_terms: D002133:Calcium Sulfate / Q000737:chemistry; D003460:Crystallization; D008956:Models, Chemical; D013055:Spectrophotometry, Infrared
chemical_list: D002133:Calcium Sulfate