A given JT problem will have a particular point group symmetry, such as T d symmetry for magnetic impurity ions in semiconductors or I h symmetry for the fullerene C 60. JT problems are conventionally classified using labels for the irreducible representations (irreps) that apply to the symmetry of the electronic and vibrational states. For example, E ⊗ e would refer to an electronic doublet state transforming as E coupled to a vibrational doublet state transforming as e.