Diairesium (greek διαίρεση, ‘split’) is the first element to exhibit the splitting phenomenon.

The electron configuration of diairesium begins 1s42s42p203s43p204s4 (ischyrosium). The 57th electron will reside in either the 3d0 or 3d1 orbital. As the energy difference between them is only 0.07 eV, at normal temperatures diairesium contains electrons in both orbitals.

As a result of its electron configuration, diairesium has unusual electronic properties.