Mössbauer spectroscopy study of iodine and tellurium atoms in solid argon

Mössbauer effect studies were performed on the nucleogenic ¹²⁵Te and ¹²⁹I monomers formed by the decay of their respective parents ^125mTe and ^129mTe embedded in solid argon at 4.2 K. Rare-gasmatrix-isolation (RGMI) and ion implantation techniques were combined to produce those extremely diluted Mössbauer emitters. The ¹²⁵Te spectrum is composed of a quadrupole split component with splitting e²qQ 2 = 9.2(4) mm s and isomer shift IS = + 0.35(5) mm s, and a single line component with IS = +0.15(5) mm s with respect to a ZnTe absorber. They are attributed to Te⁰ and Te^-1 species, respectively. The ¹²⁹I spectrum is composed of a single quadrupole split component with e²qQ = -685(20) MHz and IS = +0.75(4) mm s with respect to a ZnTe source. This species is attributed to I⁰. Two novel single-line absorbers with high f values at RT were developed for the Te and I experiments, e.g. Mg₃TeO₆ and Na₅IO₆. Based on our results for Te⁰ and Te^-1 and on relativistic Dirac-Slater atomic calculations, a new IS calibration curve under the form of a nonlinear relationship of IS versus the number of p holes (h_p) in the closed shell configuration of 5s²5p⁶ is established for ¹²⁵Te. The IS data of the I⁰ monomer are used to refine the IS(h_p) relationship for ¹²⁹I. From these new calibration curves values are deduced for the change in mean-squared charge radius Δ〈r²〉 = 3.4(3) 10^-3 fm² for ¹²⁵Te and Δ〈r²〉 = 19.9(7) 10^-3 fm² for ¹²⁹I, respectively. The origin of the quadrupole interaction and the experimental features of this RGMI-implantation-Mössbauer emission spectroscopy are fully discussed.