Refined theoretical values of field and mass isotope shifts in thallium to extract charge radii of Tl isotopes.

Electronic factors for the field and mass isotope shifts in the 6p P → 7s S (535 nm), 6p P → 6d D (277 nm), and 6p P → 7s S (378 nm) transitions in neutral thallium were calculated within the high-order relativistic coupled cluster approach. These factors were used to reinterpret previous experimental isotope shift measurements in terms of charge radii of a wide range of Tl isotopes. Good agreement between theoretical and experimental King-plot parameters was found for the 6p P → 7s S and 6p P → 6d D transitions.