Abstracts Earth and Environmental Sciences

Infrared spectra and geometry of matrix isolated rare-earth and IIIB metal fluorides

by Robert Dee Wesley

The infrared absorption spectra (40-800 cm?????) of the trifluorides of Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Tb, Ho, Er, Tm, and Yb isolated in solid argon, krypton and nitrogen matrices have been obtained. For PrF??? the symmetric and asymmetric stretching modes were observed; PrF??? is accordingly assigned a pyramidal configuration. All of the other molecules, except NdF???, exhibited only the asymmetric stretching mode and hence are assigned a planar configuration. At present, the spectrum of NdF??? cannot be satisfactorily interpreted, but a number of possibilities are explored. The low frequency modes, v??? and v???, were also observed for Sc-, Y-, La-, Ce-, Pr-, Nd-, Sm-, Eu-, Ho-, and YbF???, Using a valence force field approximation, force constants have been derived from the measured fundamental frequencies and the infrared inactive symmetric stretching frequency of many of the planar molecules has been estimated. For several of these compounds statistical entropies have also been calculated from the vibrational data and molecular geometries and are compared with Third Law values.