Scanning-tunneling-microscopy-active empty states on the (benzene + CO)/Rh(111) surface investigated by inverse photoemission

The unoccupied electronic states of the benzene + CO coadsorption system on Rh(111) have been investigated by inverse photoemission spectroscopy. The benzene and CO derived lowest unoccupied molecular orbitals ($e_{2u}$ and $b_{2g}$ for benzene and 2${\pi }^{\mathrm{*}}$ for CO) have been identified in the region 2.3–6.5 eV above the Fermi level. For the ordered (3×3) benzene + CO surface indications of enhanced density of states (DOS) within 0.5 eV of the Fermi level are found. This enhancement of the DOS may be associated with hybridized metal-benzene states, which have been invoked to be involved in the imaging process of the molecular entities in a recent scanning-tunneling-microscopy investigation of this system.