Mössbauer Effect in Molecular Iodine Crystals

Abstract

The M\"ossbauer effect of the 26.8-keV transition in ${\mathrm{I}}^{129}$ has been studied in molecular iodine crystals. From the quadrupole splitting of the transitions the ratio $\frac{{Q}_{26.8}}{{Q}_{\mathrm{gnd}}}$, the quadrupole coupling ${e}^{2}q{Q}_{\mathrm{gnd}}$, 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 ${\mathrm{I}}_{2}$ 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 $f(\ensuremath{\theta})$. The ${\ensuremath{\Theta}}_{\mathrm{D}}$ of the ${\mathrm{I}}_{2}$ crystal, as well as that of the KI crystal, are derived from the temperature dependence of the recoilless fraction.