Issue |
J. Chim. Phys.
Volume 90, 1993
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Page(s) | 1615 - 1625 | |
DOI | https://doi.org/10.1051/jcp/1993901615 | |
Published online | 29 May 2017 |
Vibrations de la molécule C60
Laboratoire de spectrométrie de vibrations, Université de Nancy I, BP 239, 54506 Vandœuvre-lès-Nancy Cedex, France.
Les vibrations de la molécule C60, qui a la symétrie Ih de l'icosaèdre régulier, sont analysées. Un calcul de fréquences est discuté pour les deux vibrations totalement symétriques (Ag), qui impliquent seulement les élongations des deux types de liaisons carbone-carbone de la molécule. On démontre qu'il est impossible de rendre compte des fréquences expérimentales attribuées à ces modes en négligeant toute interaction entre les 90 coordonnées d'élongation. Ce résultat explique des désaccords systématiques signalés dans la littérature. De plus, on établit que la constante de force d'interaction entre les deux jeux de liaisons est positive.
Abstract
The vibrations of a С60 molecule with the symmetry Ih of a regular icosahedron are analysed. A frequency calculation is discussed for the two totally symmetrical (Ag) vibrations, which involve only the stretching of the two types of carbon-carbon bonds of the molecule. It is proved that the experimental frequencies assigned to these modes cannot be accounted for by neglecting any interaction between the 90 stretching coordinates. This result explains some discrepancies currently displayed in the literature. It is shown that the interaction force constant between the two sets of bonds is positive. The force constants Fr = 5.5 aJ Â-2 for the bonds within a five-member ring, Fr' = 6.7 aJ Â-2 for the bonds connecting two five-member rings and the interactions frr = 0 and frr' = 0.5 aJ Â-2 are proposed. The last value involves an increase of the double bond characters in two five-member rings when the bond between them is stretched. This calculation appears as an attractive training example of molecular symmetry application.
Key words: C60 Fullerene / Icosahedron symmetry groups / Vibration spectroscopy / Stretching normal modes / Force field
© Elsevier, Paris, 1993