Spin-orbit effects in fullerenes

It is shown that spin-orbit effects on fullerene pi states can be treated by the model Hamiltonian xi(eff)l . s, where xi(eff) is an effective spin-orbit constant. The orbital angular momenta of the degenerate pi slates are comparable to those of atoms, and substantial magnetic dipole mixing of different pi states occurs, but xi(eff), which is proportional to the surface curvature and resulting nonzero overlaps of pi and sigma orbitals on adjacent atoms, is much less than the atomic carbon value. The predicted negative sign of xi(eff) is supported by some of the electron spin resonance results on fullerene ions and triplet states.