Molecular vibrations of rare earth trihalide dimers M2X6 (M=Ce, Dy; X=Br, I)

Abstract

The molecular geometries and vibrational spectra of selected rare earth trihalides (CeBr3, CeI3, DyBr3, DyI3) and their dimers were computed using second-order Møller–Plesset perturbation theory (MP2) and relativistic effective core potentials (RECP). The characteristics of the molecules were compared with respective data of analogous yttrium halides computed at the same level of theory. Observed trends in the molecular geometry are in agreement with the variation of ionic radii in the lanthanide row. The ab initio vibrational analyses indicate that characteristic bands of the dimers appear in non-crowded regions in the spectra of the monomers. Based on the present results, spectral features from dimers can be unambiguously identified in the vibrational spectra of rare earth trihalides.