Observation of charge-transfer states for pyridine chemisorbed on Ag(111)

The excited states of chemisorbed pyridine on Ag(111) have been determined with use of electron-energy-loss spectroscopy. In addition to weakly perturbed molecular states we observe new excitations above 1.4 eV, which we identify as metal-molecule charge-transfer excitations. These new electronic states provide an explanation for several features observed in surface-enhanced Raman scattering. © 1981 The American Physical Society.