Isotope Shifts in the 7s$\rightarrow$8s Transition of Francium: Measurements and Comparison to \textit{ab initio} Theory

TL;DR

This study measures isotope shifts in the forbidden 7s to 8s transition of francium isotopes, compares experimental results with ab initio calculations, and finds excellent agreement, advancing understanding of atomic structure in heavy elements.

Contribution

It provides the first measurements of the 7s to 8s transition in francium isotopes and compares these with new theoretical calculations, validating the accuracy of ab initio methods.

Findings

Measured isotope shifts in francium isotopes for the 7s to 8s transition.

Found excellent agreement between experimental ratios and ab initio calculations.

Performed a King Plot analysis to relate field shift constants.

Abstract

We observe the electric-dipole forbidden $7s\rightarrow8s$ transition in the francium isotopes $^{208-211}$Fr and $^{213}$Fr using a two-photon excitation scheme. We collect the atoms online from an accelerator and confine them in a magneto optical trap for the measurements. In combination with previous measurements of the $7s\rightarrow7p_{1/2}$ transition we perform a King Plot analysis. We compare the thus determined ratio of the field shift constants (1.230 $\pm$ 0.019) to results obtained from new ab initio calculations (1.234 $\pm$ 0.010) and find excellent agreement.