Datensatz

Zusammenfassung

Electrons tunneling from a scanning tunneling microscope tip to individual CO molecules on Cu(111) can cause their hopping from the surface to the tip if the bias exceeds a threshold of 2.4 V. Polarization- and time-resolved two-photon photoemission identifies the underlying elementary process as intermediate population of a CO 2π* -derived level, which exhibits an ultrashort lifetime of 0.8–5 fs. From an isotope effect of 2.7 _{- 0.5} ^{+ 0.3} it can be calculated that ≈ 0.05 % of the tunneling current transiently occupies this level while a desorption of the excited molecule occurs only in 5 × 10 ^{- 9} of the cases.