Calculation of chemical shifts in the Mössbauer spectra of some tin(IV) compounds

Abstract

The Pople-Segal-Santry SCMO method is used to calculate the electronic structures of a selected series of compounds of Sn(IV) with basis sets including 5s, 5p, and 5d orbitals on tin. The occupation number of the 5s orbital of tin in each compound is correlated with their known experimental chemical shifts and an approximately linear relationship is found. The 5s electron density at the tin nucleus, calculated from the Fermi-Segré equation using a modified form of Burns' screening rules, also exhibits a linear relation with the observed shifts. The inclusion of 5d orbitals does not appear to exert a marked effect on the calculated s-electron densities. From the results the value of ΔR/R for the ¹¹⁹Sn nucleus on excitation to the 23.8 keV level is 3.5 × 10^–4. The differential contribution, due to 5s screening, of 4s electron density to the total at the nucleus is calculated for the series. Finally, the occupation numbers of the three individual 5p orbitals lead to a qualitative understanding of experimental quadrupole splitting data.