Mössbauer isomer shifts and quadrupole splittings in osmium compounds

From Mössbauer spectra of the 36.2keV and 69.5keV gamma rays of¹⁸⁹Os, isomer shifts and electric quadrupole interactions for a number of chemical compounds of osmium in the oxidation states +8, +6, +4, +3, and +2 were obtained. The results show that the dependence of the isomer shifts on the oxidation state of Os follows the general pattern established for other transition elements like Ru and Ir. A comparison of the isomer shift data with electron densities at the Os nuclei resulting from relativistic self-consistentfield calculations for free Os ions yieldsΔ 〈r²〉 36 keV]=?2.0 · 10^?3 fm² andΔ 〈r²〉 69 keV]=?0.13 · 10^?3 fm³ for the changes of the mean-square nuclear charge radius of¹⁸⁹Os. These values are in qualitative agreement with an interpretation of the low-energy level scheme of¹⁸⁹Os in terms of two rotational bands.