Experimental study of nonadiabatic core interactions in Rydberg states of calcium

Abstract

Nonadiabatic contributions to the core polarization in calcium Rydberg states have been investigated experimentally by microwave spectroscopy of $F$ and $G$ states. Transitions $4snf^{1}F_{3}\ensuremath{\rightarrow}4sng^{1}G_{4}$ have been measured for $n=23\ensuremath{-}25$. 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 ${\ensuremath{\alpha}}_{1}=87(2)$ (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.