PRESSURE-INDUCED CHARGE-TRANSFER PHASE-TRANSITION IN CRYSTALLINE C-60-ASTERISK-C10H12SE4-ASTERISK-2(CS2) MOLECULAR-COMPLEX STUDIES BY RAMAN-SPECTROSCOPY

The Raman spectra of the molecular neutral state complex C-60C10H12Se 42(CS2) [C10H12Se4, tetramethyl-tetraselenafulvalene (TMTSF)] have be en measured as a function of pressure up to 9.5 GPa at room temperatur e. The pressure dependence of the frequencies of almost all intramolec ular phonon modes exhibits irreversible changes at 5.0 +/- 0.5 GPa. Th ese changes include splitting and softening of various modes, the most characteristic being the irreversible softening by 9 cm(-1) of the A( g)(2) pentagon-pinch (PP) mode, observed upon total release of pressur e. This softening is the same as in the case of the potassium-doped fu llerene KC60. These observations are attributed to a pressure-induced irreversible phase transition, associated with the transfer of one ele ctron from TMTSF donor to C-60 acceptor molecule. (C) 1997 Elsevier Sc ience B.V.