'Lander molecules' adsorbed on Ag, Cu and Au(111)-surfaces are investigated with scanning tunneling spectroscopy at 5 K. Density functional calculations are used to analyse the experimental data. Clear spectral features are attributed to the highest occupied molecular orbital (HOMO) and a group of lowest unoccupied molecular orbitals (LUMO). The orbital energies and the HOMO -LUMO gaps of molecules at steps and on terraces differ. The experimental observations are consistent with calculated results for the local work function and charge transfer. (C) 2008 Elsevier B.V. All rights reserved.