Single crystals of Co${\mathrm{Cl}}_2$ containing tracer ${\mathrm{Co}}^{57}$ were grown by precipitation within NaCl at low temperatures. The observed Mössbauer spectrum for ${\mathrm{Fe}}^{57}$ indicates an isomer shift of 1.32±0.04 mm/sec above stainless steel and a quadrupole splitting of 1.14±0.06 mm/sec at 80°K, which is significantly less than has been observed in ionic-${\mathrm{Fe}}^{2+}$ compounds. The small splitting can be largely explained by assuming a doubly degenerate ground state with the appropriate wave functions. The measured quadrupole splitting is reduced about 20% at room temperature which can be explained by arguments analogous to those used to interpret the temperature dependence of the splittings in iron compounds. The observed angular distribution of the intensities of the two lines demonstrates that the precipitated crystals near the surface are partially aligned in their spatial orientation. The data indicate only one charge state (${\mathrm{Fe}}^{2+}$), showing that higher charge states resulting from the emission of Auger electrons reach equilibrium in less than ${10}^{-7\mathrm{}}$ sec.

• Received 12 April 1963

DOI:https://doi.org/10.1103/PhysRev.131.1410