Resonance behavior of electron scattering from nitrogen molecules adsorbed on metallic surfaces

We use the coupled angular modes theory of electron scattering from molecules to identify the important role played by substrate multiple scattering in determining the lifetime of transient negative ions in adsorbed molecules. For the ²Π_g negative ion resonance in N₂, we demonstrate the phenomenon of complete resonance quenchingwhich occurs when the resonance energy is such that the probe electron is strongly reflected from the substrate. This situation may occur when the resonance energy lies in a band-gap of the unoccupied states of a metallic substrate. It is proposed that the simple resonance energy shift and lifetime reduction observed in previous experimental and theoretical studies of resonance electron scattering from adsorbates is by no means a universal phenomenon. The importance of the unoccupied metallic band structure of the substrate in determining the properties of negative ions in adsorbed molecules is discussed.