Hyperfine interactions in homonuclear diatomic molecules and u-g perturbations. I. Theory

Abstract
The hyperfine interactions in heavy homonuclear diatomic molecules are studied theoretically. The general matrix element of the related Hamiltonian is derived in the general case and detailed in the case of an ensemble of electronic states sharing the same dissociation limit. The predicted hyperfine perturbation effects are illustrated through the example of the iodine B state. In particular a mixing of the B 0+u state with a 1g state is to be expected near the dissociation limit. As the calculation methods apply to any non-zero nuclear spin homonuclear diatomic molecule, similar u-g symmetry breakings are likely to be met in other molecules