Effects of configuration interaction on atomic hyperfine structure

The effects of configuration interaction on hyperfine structure (h. f. s.) are considered using second-order perturbation theory. Within a given LS term, these are represented by multiplying the radial quantity < r -3 >, for each of the three orbit-dependent parts of the h.f.s. hamiltonian, by a different factor (1 + Δ). The analysis is limited to those configurations in which the only electrons not in closed shells are those of the type ( nl ) N . We treat separately the excitation of (1) a closed-shell electron into an unoccupied shell n 'l'; (2) an electron nl into an unoccupied shell n 'l' ; and (3) a closed-shell electron into the occupied shell nl . Effective operators are introduced. In cases (2) and (3), where the quantities Δ l , Δ s C , and Δ q (corresponding to the three parts of the h. f. s. hamiltonian) depend on the LS term under study, some tables are given (for d N and f N ). Because of a remarkable structure that these tables possess, it is possible to make predictions concerning the effects of configuration interaction on the three parts of the effective h. f. s. hamiltonian without requiring a detailed knowledge of radial integrals. Results consistent with the experimental data for the 3d shell are obtained. The effects of departures from perfect LS coupling are discussed.