Collisional shifts of hyperfine resonances of ground-state atoms calculated with modified pseudopotential and orthogonalization

Hyperfine splitting frequency shifts of paramagnetic atoms (H, Li, Na, K, Rb, and Cs) induced by noble-gas collisions are calculated by perturbation theory. The finite sizes of the core orbitals of noble-gas atoms (He, Ne, Ar, Kr, and Xe) are taken into account by the modified pseudopotential. The wave function of the valence electron is orthogonalized to the core orbitals, leading to a correct calculation of the resonance frequency. Fitting results are compared for the wave function bases and the core orbital sizes. The best fits are obtained when the Hartree–Fock–Roothaan wave function is used for the ground state of paramagnetic atoms and when repulsion forces due to the outermost occupied orbitals of noble-gas atoms are considered. For all combinations of alkali-metal and noble-gas atoms, the obtained fitting parameters are close to the pseudopotential height of approximately 2.6 times the atomic radius.