Theory of single molecule vibrational spectroscopy and microscopy

We have carried out a density functional study of vibrationally inelastic t unneling in the scanning tunneling microscope of acetylene on copper. Our a pproach is based on a many-body generalization of the Tersoff-Hamann theory . We explain why only the carbon-hydrogen stretch modes are observed in ter ms of inelastic and elastic contributions to the tunneling conductance. The inelastic tunneling is found to be efficient and highly localized in space without any resonant interaction and to be governed by a vibration-induced change in tunneling amplitude.