Resolving high order icosahedral tensor interactions in C60 fullerenes

C60's stiff bonds and high symmetry provide the unique opportunity to study a large polyatomic molecule (60 atoms) in individual ro-vibrational states at a temperature of ∼100 K. Simultaneously, the thermal occupation of 100's of rotational states reveals extensive J-dependence of rotational perturbations, elucidating the interplay of angular momentum, symmetry, and rovibrational coupling in a high-symmetry molecule. While previous work established the well-resolved, regular rigid rotor-like R-branch spectrum in the 8.4 μm vibrational band, the P-branch appeared anomalously fractionated and was hitherto unresolved and unexplained. We have experimentally measured and assigned individual rotational sublevels in the P-branch and identified their origin in tensor interactions driven by the molecule's icosahedral symmetry. This constitutes the first observation of intramolecular icosahedral tensor interac tions since their initial prediction for C60 three decades ago. Additionally, we obtain strong evidence that the P-branch perturbations arise from intramolecular vibrational coupling, providing a direct window into the emergence of complexity in C60.