Molecular-Orbital Study of Mössbauer Results on Iron Dissolved in Solid Noble Gases

Molecular-orbital calculations on the iron dimer are combined with M\"ossbauer data on monomeric and dimeric iron dissolved in solid noble gases to suggest for the dimer an Fe-Fe separation somewhat over 3.99 {}, to indicate for ⁵⁷ᵐFe a nuclear quadrupole moment of +0.20±{}0.03 b, and to support the choices of 9.1a₀^-3 and 6.7a₀^-3 for the electron densities produced at the nucleus of an iron atom by a pair of $4s$ electrons in configuration 3d⁶ 4s² and by a single $4s$ electron in configuration 3d⁶ 4s, respectively.