Mössbauer study of rare-gas-matrix isolatedTe125dimers,Te125F6, andTe125Cl4molecules

The Mössbauer absorption spectra of ${}_{}{}^{125}{}_{}{}^{}\mathrm{Te}$ ${\mathrm{F}}_6$, ${}_{}{}^{125}{}_{}{}^{}\mathrm{Te}$ ${\mathrm{Cl}}_4$, and ${}_{}{}^{125}{}_{}{}^{}\mathrm{Te}_2^{}{}_{}{}^{}$ molecules isolated in rare-gas matrices have been measured at 4.2 K. The matrix-isolated Te${\mathrm{F}}_6$, Te${\mathrm{Cl}}_4$, and ${\mathrm{Te}}_2$ molecules have isomer shifts of -(1.54±0.05), (1.0±0.1),and +(0.34±0.07) mm/sec relative to the Cu-${}_{}{}^{125}{}_{}{}^{}\mathrm{Sb}$ source, respectively. The ${\mathrm{Te}}_2$ spectrum shows a quadrupole splitting (QS) of 9.60±0.07 mm/sec, which contains a small asymmetry that is interpreted as an anisotropy in the Debye-Waller factor. Matrix-isolated Te${\mathrm{Cl}}_4$ shows an unresolved QS of 3.5±0.1 mm/sec. Results of Dirac-Fock calculations of electron densities at the nucleus in free atoms and ions of tellurium are given. These densities are combined with the measured isomer shifts to calculate the change in the mean-square nuclear-charge radius, $\Delta 〈r^2〉$. Values ranging from $\Delta 〈r^2〉=(2.0\mathrm{}\pm 0.4)\times {10}^{-3\mathrm{}}$ ${\mathrm{fm}}^2$ to $\Delta 〈r^2〉=(3.4\mathrm{}\pm 0.7)\times {10}^{-3\mathrm{}}$ ${\mathrm{fm}}^2$ result depending on the assumption of the electron configuration of tellurium in Te${\mathrm{F}}_6$.