${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}_{}^{+}{}_{}{}^{}\left(3\mathrm{}{d}^{6}4s\right)$ ions have been produced by uv irradiation of a xenon matrix containing 0.65% ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$. The stabilization of these ions was accomplished by mixing ∼1% of HI into the Xe matrix gas. The Mössbauer isomer shift of the ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}_{}^{+}{}_{}{}^{}\left(3\mathrm{}{d}^{6}4s\right)$ resonance is + 0.26 ± 0.03 mm/sec against iron metal at 300 K. From this we obtain the ratio of the electron densities at the ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ nucleus, $\frac{[\rho {\mathrm{}\left(0\right)\mathrm{}}_{3d^{6}4s^2}-\rho {\mathrm{}\left(0\right)\mathrm{}}_{3d^6}]}{[\rho {\mathrm{}\left(0\right)\mathrm{}}_{3d^{6}4s}-\rho {\mathrm{}\left(0\right)\mathrm{}}_{3d^6}]}=1.80\mathrm{}\pm 0.15$.

• Received 13 June 1974

DOI:https://doi.org/10.1103/PhysRevLett.33.480