Molecular structure of rare earth trihalides according to electron diffraction and spectral data

The results of electron-diffraction and spectral researches of rare earth trihalogenides are considered. The available electron diffraction data are analyzed on the basis of more advanced techniques which was followed by specification of certain internuclear distances and oscillation amplitudes. The results of studying praseodymium, gadolinium and holmium trifluorides investigated by the electron diffraction method for the first time, are given. Parameters of equilibrium geometrical configurations and estimates of force constants in the harmonic approximation are obtained for all compounds in addition to thermally average characteristics. the caclulated oscillation frequencies are compared with the literary data. Regular changes in structural parameters in series of similar rare earth trihalogenides are found which permits to specify available estimates of internuclear distances in molecules of rare earth trihalogenides not investigated experimentally