The role of electron-electron interaction beyond the restricted Hartree-Fock approximation, particularly the exchange core polarization effect, is shown to be crucial for explanation of the experimentally measured hyperfine interaction in the ($1s^{2}2s;{}_{}{}^2{}_{}{}^{}S$) state of the lithium like stripped fluorine atom (${\mathrm{F}}^{+6\mathrm{}}$). Results are presented for the entire series of such atoms from ${\mathrm{Li}}^0$ to ${\mathrm{Ne}}^{+7\mathrm{}}$ and for the excited ($1s^{2}3s;{}_{}{}^2{}_{}{}^{}S$) and ($1s^{2}2p;{}_{}{}^2{}_{}{}^{}P$) states of ${\mathrm{F}}^{+6\mathrm{}}$. The significance of the trends in these hyperfine constants is discussed. A prediction is made of the hyperfine constant in the ground electronic state of sodium like ${\mathrm{Ca}}^{+9\mathrm{}}$, which is amenable to time-of-flight measurements.

• Received 19 November 1975

DOI:https://doi.org/10.1103/PhysRevA.13.1983