Mössbauer Effect in Compounds of 127I

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Abstract
The Mössbauer effect of the 57.6‐keV transition to the ground state of 127I, which follows the β decay of 127Tem, is used to measure the isomer shifts of a variety of compounds at 4.2°K. A comparison of the shifts with the quadrupole couplings in KICl2, KICl4, ICl, and I2 indicates no detectable contribution from iodine s orbitals to the bonds. A shift of 0.56 mm/sec is observed per p electron removed from the closed‐shell I− configuration. With the aid of a shielding constant derived by Hafemeister, DeWaard, and DePasquali, one finds a shift of −2.8 mm/sec per s electron removed. With this, the orbital populations on iodine in IO4− and IO65− are determined from their shifts. It is found that localized sp3d2 hybrids for the latter lead to an unreasonable charge on the iodine while a delocalized description does not demand iodine 6d orbitals and can be made to give a reasonable result. For the tetrahedrally bonded IO4−, either description suffices and gives an acceptable answer. It is shown that frozen aqueous hydriodic acid is highly ionic while the condensed anhydrous substance is mainly covalently bonded. The substance produced when the Te in Te(OH)6 undergoes beta decay and subsequently emits the γ ray of interest is found to be mainly IO65− as shown by their relative shift. The large recoilless fractions found for telluric acid and the paraperiodate ion are attributed to the large ionic charge in a simple analysis.