Isotopic and isomeric effects in high-pressure hydrogenated fullerenes studied by Raman spectroscopy

Raman spectra of hydro- and deuterofullerenes, C60H36 and C60D36, prepared under hydrogen or deuterium pressure of 3.0 GPa at different conditions of temperature and hydrogenation time, have been measured at room temperature and normal pressure. Spatially resolved micro-Raman study shows that the ho mogeneity and optical properties of the samples depend primarily on the syn thesis temperature. The Raman spectrum of hydrofullerence contains a large number of prominent peaks originating from the various isomers. The compari son of the experimental data with results of molecular dynamics calculation s shows that various isomers are present in the samples, with the most abun dant of them being the ones with symmetries S-6, T and D-3d. The Raman spec trum of the deuterofullerence is similar in structure to that of the hydrof ullerene, however, significant differences occur in the frequency positions of the C-H and C-D stretching and bending modes which are expected from th e isotopic effect. In particular, the isotopic shift ratio for the stretchi ng mode, Omega (H)/Omega (D) approximate to 1.32, is smaller than the expec ted one from the mass ratio for pure C-H and C-D stretching modes. (C) 2001 Elsevier Science B.V. All rights reserved.