The hyperfine structure splitting and the isotope shift in the ,~ = 266 nm transition of Pt isotopes within the mass range 183 _< A ~< 198 have been determined by Resonance Ionization Mass Spectroscopy (RIMS) in combination with Pulsed-Laser Induced Desorption (PLID). The Pt isotopes were obtained at the on-line isotope separator ISOLDE-3/CERN as daugthers of the primarily produced Hg isotopes. Magnetic moments, quadrupole moments, and changes in the mean-square charge radii are deduced and compared with results of a particle-triaxial rotor model and mean field calculations. Good agreement with experimental data (including nuclear level schemes and transition probabilities) can only be obtained if triaxial shape is admitted. The calculations yield a smooth transition in the shape of odd-A Pt nuclei from a slightly deformed, nearly oblate ~95pt via triaxial 193-187pt to a strongly deformed nearly prolate t77pt.

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Resonance ionization mass spectroscopy (RIMS) and pulsed-laser induced desorption (PLID) have been combined in order to study the isotope shift ( IS ) and hyperfine structure ( HFS ) of lS4Au ( TI/= = 53 s) and ;SSAu ( Tl12 = 42 s) in the 6s aS1/2 + 6p =P1/= (A = 267 nm) transition. The Au isotopes were obtained as daughters in the decay of ls4aSaHg produced and mass separated at the new ISOLDE-3 facility at CERN. It was found that the strong deformation f12 ~ 0.25 setting in at *SSAu persists down to lSaAu.

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