Electron-molecular vibration coupling effect on the Raman spectrum of organic charge transfer salts

Abstract
Vibrational spectra of dimerized and tetramerized radical clusters have been calculated to understand the features of electron-molecular vibration (EMV) coupling effects for the charge ordered system (CO). The calculated spectra show that the totally in-phase Raman band, which is usually used as a measure of the molecular ionicity, approaches to the frequency corresponding to the average molecular ionicity in the cluster, with increasing the EMV coupling constant. On the other hand, when large charge disproportionation (CD) presents, vibronic bands show steep shift for small variation of the CD ratio. These results suggest that concerning to the normal modes with a large EMV coupling constant, we should focus on the frequency of the vibronic bands instead of the totally in-phase mode to discuss the charge distribution. Key words. Charge ordering - charge disproportionation - Raman spectroscopy - vibrational spectroscopy