Volume-corrected isomer shifts of transition-metal impurities: An orbital electronegativity scale

It is shown that, once volume effects are accounted for, a universal curve describes the Mössbauer isomer shifts of ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$, ${}_{}{}^{99}{}_{}{}^{}\mathrm{Ru}$, ${}_{}{}^{181}{}_{}{}^{}\mathrm{Ta}$, ${}_{}{}^{193}{}_{}{}^{}\mathrm{Ir}$, ${}_{}{}^{195}{}_{}{}^{}\mathrm{Pt}$, and ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ impurity nuclei in a variety of hosts. The curve defines an "orbital" electronegativity associated with non-$d$ electron charge flow on or off these transition-metal atoms in alloys. The shape of the curve is remarkable in the extent to which it agrees with the "total" electronegativity scales of Pauling, Gordy-Thomas, and others. This agreement suggests that $d$ and non-$d$ charge flow are simply proportional to one another to an extent we find surprising.