Isotope shifts of 6s5d³D-6s6p¹P₁ transitions in neutral barium

First laser spectroscopic measurements of the 6s5d³D ₁-6s6p¹P₁ and 6s5d³D ₂-6s6p¹P₁ transitions in several isotopes of atomic barium have been performed. The hyperfine structure of these transitions was optically resolved and isotope shifts for even and odd isotopes were determined. The isotope shifts show a deviation from their expected behavior for odd isotopes in an analysis based on King-plots. This observation puts atomic structure calculations at test because available theories do not predict this. A profound understanding of the wavefunctions for heavy alkaline earth systems like barium (Ba) and radium (Ra) is essential for a theoretical evaluation of their sensitivity to fundamental symmetry breaking effects such as they could be observed, e.g., through permanent electric dipole moments. Further the absolute frequency of the 6s^{2 1}S₀-6s6p ³P₁ intercombination line in ¹³⁸Ba was determined to be 12∈636.6232(1) cm^-1.