CRYSTAL-FIELD INDUCED MIXING OF ELECTRON-STATES IN C-60 CRYSTALS AT HIGH-PRESSURE

Optical absorption spectra of thin fullerene (C-60) crystals in the ra nge 1.7 to 3.8 eV have been measured at T=300 K and at pressures up to 2.5 GPa. The spectrum shifts toward the red with pressure, and the el ectron absorption intensity is redistributed among its bands. The inte nsity of the band associated with the lowest direct electron interband transition monotonically increases with pressure, whereas the intensi ty of the upper interband feature decreases. Bands related to weak edg e absorption in the range between 1.7 and 2.2 eV gradually merge with the band associated with the lowest interband transition, whose intens ity rises with pressure. A similar redistribution of intensity among e lectron transition bands has been observed when comparing the spectrum of an isolated C-60 molecule and that of a C-60 crystal. The results indicate that the crystal-field induced mixing of electron states is p resent in solid C-60, and they can be discussed in terms of the Craig- McClure model, which was suggested to describe crystal-field induced m ixing of electron states in anthracene and naphthalene molecular cryst als. (C) 1998 American Institute of Physics.