Fine structures of the resonant Raman spectra in quasi-one-dimensional crystals of halogen-bridged mixed-valence platinum compounds

The resonant Raman spectra due to the symmetric Cl-Pt-Cl stretching mode in (Pt(en) 2 )(Pt(en) 2 Cl 2 )(ClO 4 ) 4 and (Pt(en) 2 )(Pt(en) 2 Br 2 )(ClO 4 ) 4 single crystals have been observed to be resolved into fine structures with three main components at 2K. It is found that both the Raman frequencies and the relative intensities of these components depend considerably on the incident photon energy and on the order of the overtone. The origin of the fine structures is discussed from the detailed measurements of this dependence.