engleski

Femtosecond time-resolved two-photon photoemission spectroscopy of C6H5X/D2O/Cu(111)

The electron dynamics at a metal-molecule interface is studied with time-resolved two-photon photoemission. We report here energies, workfunction changes and lifetimes of excited electronic states in amorphous D2O/Cu(111) and coadsorbed C6H5F systems after optical excitation with 3.8 eV + 1.9 eV femtosecond laser pulses. We observe a decrease in lifetime of the solvated electron state from 90±5 fs for bare D2O to 60±5 fs for coadsorbed C6H5F. Further, after a total estimated exposure to 0.5×106 photons per C6H5F molecule, a workfunction change of 200±50 meV was observed. Due to the absence of photo-induced workfunction changes in the single stack D2O/Cu(111) and C6H5F/Cu(111), this change is concluded to be mediated by solvated electrons. Additional experiments on C6H5Cl/D2O/Cu(111) were performed and an even larger photoinduced workfunction change was observed. The increase in workfunction is explained by the formation of F−/Cl− as a photo-chemical dissociation product. We conclude to have identified the charge transfer to C6H5F(/Cl) and a fingerprint of its photoinduced dissociation. Future experiments aim to systematically change the UV photon energy and the molecule acceptor level.

photoemission spectroscopy

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