Role of Deformation in the Intrusion of theh92Levels below theZ=82Proton Shell

The hyperfine structure and isotope shifts of ${}_{}{}^{189,191,193}{}_{}{}^{}\mathrm{Tl}_{}^m{}_{}{}^{}$ and ${}_{}{}^{193}{}_{}{}^{}\mathrm{Tl}$ have been observed by means of collinear atom beam laser spectroscopy. Deduced deformations for the ${\frac{9}{2}}^{-}$ isomers are larger than for the ${\frac{1}{2}}^{+}$ ground states and increase with decreasing neutron number. This explains a strong neutron-number dependence of the odd-proton energy levels in these nuclei near the $Z=82\mathrm{}$ shell closure. Despite different deformations, rotational properties are nearly identical in ${}_{}{}^{185-199}{}_{}{}^{}\mathrm{Tl}$. Microscopic theory ascribes this to a systematic balance between changing deformation and neutron pairing.