IN-SITU HIGH-RESOLUTION FT-IR STUDY OF THE ORIENTATIONAL PHASE-TRANSITION IN C-60 FILM

We have studied the orientational phase transition of a water-free C-60 film by examining the temperature dependence of line shift, half-width, acid integrated absorbance of the four fundamental IR-active modes in the C-60 film with high-resolution (0.25 cm(-1)) Fourier transform infrared (FT-IR) spectroscopy. A discontinuous line shift of the IR-active mode at 576 cm(-1) is observed at about 257 K for the first time. This temperature is consistent with the previous results that the orientational phase transition of C-60 bulk structure occurs at 250-262 K. In addition, the temperature dependence of the line shift for the IR-active mode at 526 cm(-1) is the opposite of those for the other modes. The reason for this difference can be explained qualitatively on the basis of the relation between the intermolecular interaction and the motion of atoms for each IR mode.