Enhanced conductance of molecular states at interstitial sites

Arrays of phthalocyanine molecules on Pb(100) are investigated with scanning tunneling microscopy. Maps of the differential conductance exhibit drastic changes as the sample voltage is being varied. Maximal conductances are observed at positions between the molecules mimicking bonding states. However, the maxima are shown to result from a superposition of non-interacting states. We expect that this effect may be observed from many other molecules.