J. Phys. I France 2 (1992) 2097-2105
Absorption spectra of crystalline fullerite 60 at pressures up to 19 GPaK. P. Meletov, V. K. Dolganov, O. V. Zharikov, I. N. Kremenskaya and Yu. A. Ossipyan
Institute of Solid State Physics, Russian Academy of Sciences, 142432, Chernogolovka, Moscow distr., Russia
(Received 2 July 1992, accepted 30 July 1992)
The absorption spectra of the thin fullerite crystals, C60, have been measured in the energy range 1.1-3.1 eV at room temperature and pressures up to 19 GPa. The mean rate of the spectral pressure shift d has been estimated for strong- and weak-absorption regions. It has been found that in the strong-absorption region its value at normal pressure is -0.15 eV/GPa, and then its absolute value decreases to 0.019 eV/GPa at 12 GPa. The weaker-absorption region located, under normal pressure, at the red edge shifts much more slowly ( eV/GPa) and coalesces with the strong-absorption region at pressures exceeding 2.0 GPa. The T=4.2 K measurements indicate the presence of a fine structure in the weak-absorption region of fullerite 60, that transforms to a step at room temperature. The dependence of the weak-absorption edge shift on the intermolecular distances has been determined and shown to be governed by the Van der Waals forces of the intermolecular interaction.
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