Cascade Anticrossing Measurement of the Anomalous Hyperfine Structure of the4D2State of Rubidium

A new technique, cascade anticrossing spectroscopy, has been developed to determine the effective values of $〈r^{-3\mathrm{}}〉$ for the spin-dipole, orbital, contact, and quadrupole hyperfine interaction terms for the $4{}_{}{}^2{}_{}{}^{}D$ state of Rb. They are, in units of ${10}^{24}$ ${\mathrm{cm}}^{-3\mathrm{}}$, ${〈r^{-3\mathrm{}}〉}_d=-0.36\mathrm{}\left(8\right)\mathrm{}$, ${〈r^{-3\mathrm{}}〉}_l=+0.20\mathrm{}\left(2\right)\mathrm{}$, ${〈r^{-3\mathrm{}}〉}_c=-4.3\mathrm{}\left(1\right)\mathrm{}$, and ${〈r^{-3\mathrm{}}〉}_q=+0.79\mathrm{}\left(66\right)\mathrm{}$, respectively. The negative value of ${〈r^{-3\mathrm{}}〉}_d$ and the unexpectedly large value of ${〈r^{-3\mathrm{}}〉}_c$ are surprising. The fine-structure splitting has been measured to be - 13 360.9(8) MHz.