199Hg Mössbauer measurements on mercury alloys and Hg-fluorides

The Mössbauer effect on the 158 keV 5/2^??1/2^? transition in¹⁹⁹Hg, of the order of 10 ppm, has been studied using the current integration technique. The isomer shift between the Hg(I)- and Hg(II)-fluorides as well as the quadrupole splitting in Hg₂Pt and Hg₂F₂ are interpreted in terms of relativistic Hartree-Fock-Slater and Molecular Orbital calculations. The following nuclear parameters could be derived: δ2<=(3.2± l.l)10^?3fm² andQ(5/2^?)=(-0.8±0.4)b. Evidence for an oblate triaxially deformed¹⁹⁹Hg nucleus is derived from particle plus rotor calculations.