Dynamics of Electron-Induced Manipulation of Individual CO Molecules on Cu(111)

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.