Polarized resonance Raman spectra of hexahalide complexes of transition metals: The effect of electronic degeneracy on the polarization of vibrational Raman scattering

摘要

Polarized vibrational resonance Raman spectra have been measured for eight hexahalide complexes of transition metals, lowhyphen;spind4OsCl62minus;, OsBr62minus;, and lowhyphen;spind5IrCl62minus;, IrBr62minus;, and lowhyphen;spind6PdCl62minus;, PtCl62minus;, PtBr62minus;, and PtI62minus;. Polarization anomaly due to asymmetric Raman tensor was found for thed5complexes, whereas such was not observed in the cases of thed4andd6complexes. The result is analyzed on the basis of a symmetry consideration in vibronic space. Electronic and/or vibrational degeneracy is shown to induce the antisymmetric part of vibrational Raman tensors. It is concluded that the former is primarily responsible for the polarization anomaly found for thed5complexes. Under resonance conditions, the hot transitions originating from the excited levels of degenerate vibrations can give different Raman tensor patterns from those for the corresponding 1larr;0 transitions. It is stressed that the selection and polarization rules of vibrational Raman scattering should be discussed in relation to the transition and not to the vibrational mode involved in it.