VIBRATIONS OF A C-60 MOLECULE

The vibrations of a C60 molecule with the symmetry I(h) of a regular i cosahedron are analysed. A frequency calculation is discussed for the two totally symmetrical (A(g)) vibrations, which involve only the stre tching of the two types of carbon-carbon bonds of the molecule. It is proved that the experimental frequencies assigned to these modes canno t be accounted for by neglecting any interaction between the 90 stretc hing coordinates. This result explains some discrepancies currently di splayed in the literature. It is shown that the interaction force cons tant between the two sets of bonds is positive. The force constants F( r) = 5.5 aJ angstrom-2 for the bonds within a five-member ring, F(r') = 6.7 aJ angstrom-2 for the bonds connecting two five-member rings and the interactions f(rr) = 0 and f(rr') = 0.5 aJ angstrom-2 are propose d. The last value involves an increase of the double bond characters i n two five-member rings when the bond between them is stretched. This calculation appears as an attractive training example of molecular sym metry application.