Evidence for a Low-Frequencyπh92Band Crossing inPt185andIr183

Evidence is presented for a $\pi h_{\frac{9}{2}}$ band crossing at surprisingly low rotational frequency in the odd-neutron ${}_{}{}^{185}{}_{}{}^{}\mathrm{Pt}$ and odd-proton ${}_{}{}^{183}{}_{}{}^{}\mathrm{Ir}$ nuclei. The proton nature of the crossing is indicated by measured $\frac{B(M1;I\to I-1)}{B(E2;I\to I-2)}$ ratios, strongly supported by theoretical values from both the semi-classical Dönau and Frauendorf approach and a variable-core particle-rotor calculation employing cranked-shell-model matrix elements. However, the actual crossing frequency is greatly overestimated by the cranking method using generally accepted model parameters.