Charge distribution and molecular arrangement in (DI-DCNQI)2Ag studied by high pressure vibrational spectroscopy

Charge distribution and molecular arrangement in (DI-DCNQI)(2)Ag have been investigated by vibrational spectroscopy. The Raman spectrum shows vibronic band of an a(g) C=N stretching mode. It appears different frequency from the IR band of the stretching mode, suggesting that the dimerized stacking is distorted into tetramerized one at low temperatures. The vibronic Raman signal is readily suppressed by pressures, indicating that no substantial charge disproportionation exists in the charge localized phase. While Coulomb interactions have been proposed as the origin for the charge localization, these results suggest that the lattice distortion also plays an important role for the ground state property.