Infra-red spectra of matrix-isolated MgF2

Abstract

Infra-red spectra of evaporated MgF₂ isolated at liquid helium temperatures in neon, argon, krypton, xenon, nitrogen and carbon monoxide matrices are reported, in contrast to previous studies, the bands at 480 and 740 cm^–1 are assigned to a dimeric molecular species, (MgF₂)₂, on the basis of the equivalent dependence of their intensities on the rate of deposition of MgF₂ vapour. No symmetric stretching vibration was observed, which suggests a linear structure of MgF₂. Deviations of the bond angle in MgF₂ from 180° calculated from isotopic splittings of the asymmetric stretching mode v₃ of MgF₂ for the different matrices are similar to those obtained from previous studies. The small differences of the calculated angle from linearity could result from an inherent inaccuracy of the isotopic shift method for bond angles near 180°.