Mass-polarization effects in the 1s2s1Sand3Sstates of helium

From a laser spectroscopic study of isotope shifts in the 1s2s ${}_{}{}^1{}_{}{}^{}$S${,}^3$S→1snp transitions in ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ and ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ and of the hyperfine structure in the 1snp Rydberg states of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ we have derived highly accurate information on mass-polarization effects in the 1s2s ${}_{}{}^1{}_{}{}^{}$S and ${}_{}{}^3{}_{}{}^{}$S states. The experimental results, which are in good agreement with recent, high-precision variational calculations, confirm an isotope dependence of 〈${\mathbf{p}}_1$⋅${\mathbf{p}}_2$〉. .AE