Fig. 3: Energy levels and molecular orbitals of allene.
From: Symmetry breaking in core-valence double ionisation of allene
Molecular energy diagram and iso-potential-energy-surfaces of the relevant orbitals. Purple energies represent core orbitals and orange energies represent valence orbitals. Ionisation from either core orbital will lead to localisation and symmetry breaking. The molecule is visualised in its neutral shape with H2 groups on each side perpendicular to each other.
