ON THE NATURE OF THE LASER IRRADIATION-INDUCED REVERSIBLE SOFTENING OF PHONON MODES IN C-60 SINGLE-CRYSTALS

The average temperature rise in the laser excitation spot of the C-60 single crystal has been determined using the Stokes to anti-Stokes int egrated peak intensity ratio for the H-g(1) phonon mode. The reversibl e softening of the A(g)(2) pentagon pinch mode was found to be due to the heating of the sample caused by the laser irradiation, in agreemen t with experimental results obtained for uniformly heated samples. The se findings are in quantitative agreement with results obtained by num erical calculations of the local temperature rise, which indicates the highly non-uniform temperature distribution in the laser excitation s pot associated with the small thermal conductivity of solid C-60. (C) 1998 Elsevier Science B.V. All rights reserved.