Electronic structure of molecular icosahedra films

Using angle-resolved photoemission and inverse photoemission, the electronic structure of films of the molecular icosahedron orthocarborane (C₂B₁₀H₁₂) on Cu(100) has been studied. The measured gap between the highest occupied molecular orbitals and the lowest unoccupied molecular orbitals is in good agreement with modified neglect of differential overlap calculations. An unoccupied exopolyhedral state has been found and is ascribed to molecular orbital hybridization. This hybridization is consistent with the observed dispersion of the orthocarborane molecular orbitals. This molecular orbital dispersion indicates a surface Brillouin zone edge with an average radius of 0.7 AA^-1, and suggests that the molecules adopt local close-packed ordering in the overlayers, with an intermolecular distance of 5.58 AA.