Low-temperature infrared spectroscopy of H2 in crystalline C60

Diffuse reflectance infrared spectroscopy is used to measure the quantum dynamics of molecular hydrogen trapped within a C-60 lattice at temperatures as low as 10 K. Crystal field effects in conjunction with rotational translational coupling lead to a rich spectrum with multiply split peaks that are more than an order of magnitude sharper than at room temperature. The induced redshifts in the vibrational-rotational mode frequencies are explained using a simple model in which the state dependence of the H-2 polarizability leads to changes in the C-60-H-2 interaction potential.