Electron-phonon coupling is an important factor in understanding many properties of the C 60 fullerides. However, there has been little success in quantifying the strength of the vibronic coupling in C 60 ions, with considerable disagreement between experimental and theoretical results. We will show that neglect of quadratic coupling in previous models for C 60 − ions results in a significant overestimate of the linear coupling constants.Including quadratic coupling allows a coherent interpretation to be made of earlier experimental and theoretical results which at first sight are incompatible.

Adsorption of C 60 on a metallic surface may be expected to result in electronic charge transfer to the organic adsorbant, even if a buffer layer is included between the C 60 molecules and substrate. Subsequently, intramolecular coupling between the molecule's electronic and vibrational degrees of freedom would be expected to result in species subject to Jahn-Teller ͑JT͒ distortions. In this work, we use Hückel molecular-orbital theory to visualize the effect that JT interactions may have on C 60 − ions imaged using scanning tunneling microscopy ͑STM͒. Several distortion symmetries and adsorption orientations are considered and the resulting simulations are compared to STM images in the literature.

The effects of molecular collisions on the hyperpolarizabilities of spherical atoms are considered. Closedform expressions are given for the second hyperpolarizability of a pair of atoms in the presence of dipolar coupling for five cases, namely, a static electric field, third-harmonic generation, electric-field-induced secondharmonic generation, the Kerr effect, and four-wave mixing. The longest range contribution to the mean hyperpolarizability varies as R-6; it is less than one-third of the magnitude of the effect deduced by Donley and Shelton, but agrees with that obtained by Hunt. For a dissimilar pair of atoms, a collision-induced first hyperpolarizability proportional to the inverse fourth power of the separation is predicted.

Using Hückel molecular-orbital theory, images are created to represent the electron distributions expected for a C 60 molecule adsorbed on a substrate. Three different orientations of the C 60 molecule on the substrate are considered. The effect of the interaction of the molecule with the substrate is treated purely from the basis of symmetry using group theoretical methods. The resulting electron distributions are then used to generate idealized images which represent how the molecule may appear when observed in a scanning tunneling microscope ͑STM͒ experiment. Comparison is made with STM images appearing in the literature. It is found that the more complicated ab initio methods usually employed to simulate STM images are not required in order to match observed results. Furthermore, we find that an unequivocal identification of the orbitals responsible for a given STM image cannot be made from analysis of the STM image alone.

Raman scattering and infrared data from experiments performed on doped fullerenes is collated from published work. The resulting information is interpreted in order to extract a measure of the electron-phonon coupling in fullerene systems. A simple model is used to analyze the shifts in the phonon frequencies caused by doping, in which contributions due to charge-transfer effects and vibronic coupling are separated. It is found that the coupling coefficients inferred for the h g modes of the buckminsterfullerene monoanion C 60Ϫ are in good agreement with those deduced from experimental photoemission spectroscopy data.