Anomalous infrared transmission of adsorbates on ultrathin metal films: Fano effect near the percolation threshold

IR absorption lines of CO on ultrathin epitaxial iron films are both enhanced and asymmetric. In this letter we show new experimental results which demonstrate a correlation of the asymmetry of the CO-stretching line to electronic properties of the underlying metal film. The new finding indicates the important role of metal film morphology for nonadiabatic effects. Such effects are strongest slightly above the percolation threshold as our results show. (C) 2000 American Institute of Physics. [S0021-9606(00)70439-9].