A comparative theoretical study of compounds of the heavy main-group Mössbauer isotopes Sn to I

Semiempirical molecular orbital calculations are applied to calculate electric field gradients V_zz and electronic charge densities ρ{variant}(0) at the nucleus for a series of tin- and iodine-containing compounds. The results are related with experimental isomer shifts δ and quadrupole splittings ΔE_q and enable an understanding of experimental Mössbauer spectra in terms of electronic structure theory. From this correlation new values for the fractional change δR/R of the nuclear radius and for the nuclear quadrupole moment Q can be derived. A careful analysis of the various contributions to V_zz and ρ{variant}(0) determines the range of applicability of commonly used phenomenological fitting schemes.