  A semi-empirical model of the infrared (IR) spectrum of the C$_{60}$ molecule
is proposed. The weak IR-active modes seen experimentally in a C$_{60}$
crystalline sample are argued to be combination modes caused by anharmonicity.
The origin of these 2-mode excitations can be either mechanical (anharmonic
interatomic forces) or electrical (nonlinear dipole-moment expansion in normal
modes coordinates). It is shown that the electrical anharmonicity model
exhibits basic features of the experimental spectrum while nonlinear dynamics
would lead to a qualitatively different overall picture.

Condensed Matter