A measurement of charge asphericity in iron metal

Electron-density distribution in metallic iron has been determined based on the reflection data measured up to sin θ/λ = 1.36 Å^-1 with Mo Kα radiation using a spherical specimen of 0.186 (6) mm in diameter. Fe is cubic, Im3m, a = 2.8652 (1) Å, V = 23.522 (3) ų, Z = 2, μ(Mo Kα) = 30.35 mm^-1 (T = 297 K). Final R was 0.007 for the 37 unique reflections, the internal agreement factor for the equivalent reflections being 0.013 for the 527 observed reflections. In the difference synthesis a positive peak of 0.7 (1) e Å^-3 was found in the [111] direction at 0.32 (1) Å from the iron nucleus and a trough of -0.6 (1) Å^-3 was found in the [100] direction at 0.54 (1) Å from the nucleus. Charge asphericity in iron metal, presumably due to the 3d electrons in t_2g orbitals, is essentially the same as that of the other 3d b.c.c. metals, V and Cr.