INFRARED ROTATION AND VIBRATION-ROTATION BANDS OF ENDOHEDRAL FULLERENE COMPLEXES - HELIUM IN C-60-DERIVED NANOTUBES

We calculate the far-infrared absorption spectrum associated with the vibrational and rotational motion of a He atom enclosed in a nanotube of diameter 0.7 nm, formed by rolling up a single sheet of graphite an d capping each end with one half of a C60 molecule. The endohedral pot ential and dipole moment are calculated using a semi-empirical atom-at om model. The spectrum is that of a perturbed two-dimensional harmonic oscillator. A strong fundamental band lies between 100-200 cm-1, and there is a much weaker third harmonic at higher frequencies.