Infrared rotation and vibration-rotation bands of endohedral fullerene complexes. He@C70

We calculate the far-infrared absorption spectrum of the endohedral fullerene He@C70. In this molecule the He inclusion experiences a strongly anisotropic potential V(p, z). The 2D Schrödinger equation governing its rovibrational motion is solved variationally. The spectrum consists of strong P-and R-branches (Δm = ± 1) and a much weaker Q-branch (Δm = 0), and peaks near 100 cm−1. Despite its apparent complexity, however, the eigenvalue spectrum is essentially regular, and the system displays little evidence of chaos.