Experimental study of nonadiabatic core interactions in Rydberg states of calcium

Nonadiabatic contributions to the core polarization in calcium Rydberg states have been investigated experimentally by microwave spectroscopy of $F$ and $G$ states. Transitions $4snf{}_{}{}^1{}_{}{}^{}F_3^{}{}_{}{}^{}\to 4sng{}_{}{}^1{}_{}{}^{}G_4^{}{}_{}{}^{}$ have been measured for $n=23-25\mathrm{}$. The transition frequencies are in good agreement with calculations based on a dynamical model of the core interaction, but differ by approximately a factor of 2 from the usual adiabatic treatment. The dipole core polarizability of calcium (the polarizability of ${\mathrm{Ca}}^{+}$) is found to be ${\alpha }_1=87\mathrm{}\left(2\right)\mathrm{}$ (atomic units). The quantum defect for the $4sng{}_{}{}^1{}_{}{}^{}G_4^{}{}_{}{}^{}$ series is 0.0310(5). General formulas are presented for the quantum defects of the high-angular-momentum states.