Gas phase spectroscopic studies of actinide-containing diatomic molecules have yielded information concerning the electronic structure and bonding of several ionically bound examples (oxides, sulfides, halides and nitrides of Th and U) . The value of studying these molecules in the gas phase is that the results can be used to evaluate the accuracy of relativistic quantum chemistry calculations, without the additional difficulties presented by condensed phase lattice or solvent-solute interactions. Gas-phase high-resolution spectroscopic determination of energy levels and properties for actinide-containing diatomic molecules also plays important roles in using these molecules as highly sensitive quantum sensors for probing fundamental physics beyond the Standard Model.