Mössbauer Effect in Molecular Iodine Crystals

The M\"ossbauer effect of the 26.8-keV transition in I¹²⁹ has been studied in molecular iodine crystals. From the quadrupole splitting of the transitions the ratio Q26.8Qgnd, the quadrupole coupling e²qQgnd, and the isomer shift are derived. The sign of the quadrupole coupling shows that the sign of the iodine field gradient is positive. From the isomer shift of I₂ and from those of alkali iodides a linear dependence of the isomer shift on the number of p holes is derived. The intensities of the peaks give a strong indication of an angular dependence of the recoilless fraction f(θ). The ΘD of the I₂ crystal, as well as that of the KI crystal, are derived from the temperature dependence of the recoilless fraction.