Infrared Absorption of Lanthanum, Scandium, and Indium Borate and the Force Constants of Borate Ion

Abstract

The infrared absorption spectra of LaBO3, InBO3, and ScBO3 have been observed as crystalline powders in the wavelength range from 7 to 20 microns. The borates had a B10/B11 ratio varying from the natural abundance (18/82) up to about 96/4. The four fundamental frequencies for B10 fell within the ranges, ω1 = 939, ω2 = 740–790, ω3 = 1265–1330, ω4 = 606–675, all in cm—1. The totally symmetric frequency, ω1 is observed only in LaBO3, which has less than threefold site symmetry, unlike the other two salts. The GVF force constants have been calculated and are compared with those of BF3. A very strong specific coupling of the out-of-plane bending mode (ω2) is observed in LaBO3, but the fine structure is not well resolved, and only a rough estimate of the coupling constant and dipole derivative can be made.