Effect of Core Excitation on the Hyperfine Structure of Rubidium

Perturbations of the ratio of hyperfine coupling constants for the $5P$ levels of rubidium are investigated. The excitation of one $4s$ electron to higher $s$ orbits is most effective in altering the ratio $\frac{a_{\frac{1}{2}}}{a_{\frac{3}{2}}}$, although the effect of $4p$ shell excitation may be perceptible. The fraction of excited $4s$ configuration in the $5P$ state is written in terms of matrix elements of the electrostatic interaction, from which it appears that the sign of the perturbation is in agreement with the discrepancy observed by Senitzky and Rabi.