Electronic structure and Mössbauer isomer shift of the iron atom isolated in a crystalline argon matrix

Multiple-scattering calculations were performed on an Fe${\mathrm{Ar}}_{12}$ cluster in order to describe the iron atom trapped in a crystalline argon matrix. The total electron densities at the iron nucleus derived from these calculations are used to interpret Mössbauer-isomer-shift data. The different bonding mechanisms contributing to the metal-atom—rare-gas matrix interaction are also investigated. It is found that the overlap distortion effect of the metal wave functions plays a major role in the calculated electron densities. The iron-isomer-shift calibration constant was found to be $-0.22\mathrm{}{a}_0^3$ mm ${\sec }^{-1\mathrm{}}$.