The UV-Vis spectra of Diels-Alder adducts of C-60 show characteristic
differences with respect to the spectra of isolated C-60. New bands ap
pear between 400 and 500 nm, as well as at around 700 nm. In order to
explain the origin of these bands we performed quantum chemical calcul
ations for model molecules: C60H2n (n=1,2,3). The upper bands correspo
nd to singlet-singlet transitions while the lowest energy band can ori
ginate only from a triplet level and spin dependent interactions shoul
d be responsible for this excitation. Symmetry arguments indicate that
such transitions remain forbidden for pure C-60.