No abstract

Polarized optical conductivity spectra in the IR and visible range and variable-temperature photoluminescence spectra of the C 60 F 18 single crystals in the 4-300 K temperature range are reported. Density-functional theory ͑DFT͒ calculations of vibrational spectra and time-dependent DFT calculations of the excitation energies of the C 60 F 18 molecule are performed to interpret experimentally observed phenomena. Orientation of the C 3v -symmetric C 60 F 18 molecules in the single crystal is revealed by comparison of the experimental polarized IR spectra and vibrational DFT calculations. A 2 symmetry is assigned to the lowest energy singlet excited state of C 60 F 18 , and hence pure electronic S 0 → S 1 excitation is found to be dipole forbidden. Fine vibronic structure found at low temperature is interpreted in terms of Herzberg-Teller and Franck-Condon mechanisms. Considerable similarity with vibronic spectra of C 60 is found and explained by presumable localization of the lowest energy electronic excitation of C 60 F 18 on the fullerenelike part of the molecule.

Homogeneous carbon-deuterium (C−D) films with a high [D]/[C] ratio, redeposited on deuteriumplasma discharge in the T-10 tokamak, have been studied by means of thermogravimetric analysis, spectroscopy based on electron paramagnetic resonance, Fourier-transform infrared spectroscopy and photoluminescence spectroscopy. Deuterium was found to be accumulated only in the C−D 2,3 sp 3 vibrational modes, including 633 and 1090 cm −1 deformation modes, and 2100-2200 cm −1 stretching modes, the intensity of which slightly diminished on annealing at 450 • C. Photoluminescence of an excitonic nature was found at 390-530 nm related to the C 2p π −π * transitions within the aromatic rings, and luminescence quenched at 450 • C. The luminescence excitation spectra at 3-10 eV showed similarity in peak positions to the luminescence excitation spectra of thin C 60 films. Possible physical reasons explaining the effect of H−D−T isotopes on the accumulation and desorption of hydrogen are considered.

No abstract

No abstract