Shape coexistence in ¹⁸⁷Au studied by laser spectroscopy

Hyperfine-structure parameters and isotope shift of the 9/2− isomeric state in 187Au relative to 197Au for the 267.6-nm atomic transition have been measured for the first time using the in-source resonance-ionization spectroscopy technique. The magnetic dipole moment and change in the mean-square charge radius for this 9/2− isomer have been deduced. The observed large isomer shift relative to the 1/2+ ground state in 187Au confirms the occurrence of the shape coexistence in 187Au proposed earlier from the analysis of the nuclear spectroscopic data and particle plus triaxial rotor calculations. The analysis of the magnetic moment supports the previously proposed 9/2−, 1/2−⁢[541] assignment at moderate prolate deformation for 187Au