1 / 24

DIET: Changes and constants in changing times.

Explore the evolution of DIET mechanisms in chemistry, focusing on adsorbates at surfaces, surface photochemistry, and breaking of bonds. Discover the interplay between localization and delocalization, and observe ultrafast charge transfer processes.

dougal
Download Presentation

DIET: Changes and constants in changing times.

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. DIET: Changes and constants in changing times. Dietrich Menzel Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin and Physik-Dept. E20, Techn. Univ. München, Garching (Germany)

  2. In memoriam Ted MadeyDistinguished scientistlongtimeClose friend frequent collaborator

  3. Early times: 1963 1973/74

  4. Gomerfest May 1996

  5. Excited state chemistry: Reactivity induced by electronically excited states Steep potential in F.C.- region couples electronic to nuclear oordinates Curve crossings can lead to nonadiabatic behavior • Adsorbates at surfaces: Coupling/bonding to surface induces changes in molecules which change reactivity in thermally accessible states (catalysis, electrochemistry, layer growth etc.) RAB

  6. EID, ESD, DIET, • Surface photochemistry: • Coupling to surface also changes excited states and introduces possible charge and energy transfer: • ÞPhotochemistry changed Concentrate on first step: Breaking of bonds (dissociation, desorption)

  7. Changes:MethodsMachines and radiation sources

  8. The heroic times : 1962-1964 Paul Redhead, Can. J. Phys. 42, 886 (1964)

  9. Today‘s uhv machinery: 10 cm 3 m

  10. Today‘s radiation sources: Behemoths 1 cm 5 m (lasers); 100 m (SR sources)

  11. Constants in understanding: Principles, mechanisms, and counteracting influences

  12. DIET mechanisms - Energy Energy Energy Z Z Z Adsorbate or substrate mediated, depending on location of primary excitation Direct Hot electron -TNI DIMET Localization vs. delocalization; steepness of potential

  13. Adsorbates on metal and semiconductor surfaces • Observations: • (For excitations by electrons or photons) • Compared to corresponding molecular processes: • Considerably more neutrals than ions(except high exc.) • Strong decreasesof cross sections, which are very sensitive to • bonding mode • type of primary excitation (valence-double valence-core- core satellite) • adsorbate density and order • defects • mass(isotope effect !!)

  14. Adsorbates on metal and semiconductor surfaces • Observations: • (For excitations by electrons or photons) • Compared to corresponding molecular processes: • Considerably more neutrals than ions(except high exc.) • Strong decreasesof cross sections, which are very sensitive to • bonding mode • type of primary excitation (valence-double valence-core- core satellite) • adsorbate density and order • defects • mass(isotope effect !!) Explanation: Competition between bond dissociationand transfer of excitation (quenching by energy and/or charge transfer): LOCALISATION vs. DELOCALISATION must be VERY fast !

  15. Direct observation of ultrafast CT processes:Laser pump-probe, and Core hole clock See, e.g., D. Menzel, Chem.Soc. Rev. 37, 2212, 2008, and cited work

  16. Some early successes: Isotope effect ESDIAD Strongly localising excitations (core, complex)

  17. Some early successes: Isotope effect ESDIAD Strongly localising excitations (core, complex) But not only DIET: The ruthenium story: TPD, LEED, Auger, DF CO (T.E.M.+D.M., Japan J. Appl. Phys. Suppl. 2 (1974) 229) O2 and CO oxid. (T.E.M., HA Engelhardt, D.M., SS 48(1975) 304) XPS: Valence bands, Satellites, CO and O w. John Fuggle, M. Steinkilberg(Phys. Lett. 51A (1975) 163; CPL 33 (1975) 233; SS 52 (1975) 521)

  18. Some recent examples: Alkalis on the moon: “Far-out surface science“ B. Yakshinsky and T.E. Madey, Nature 400 (1999) 642

  19. Some recent examples: Alkalis on the moon: “Far-out surface science“ Yakshinsky and Madey, Nature 400 (1999) 642 Water on Ru(0001): Extreme radiation sensitivity N.S. Faradzhev, K.L. Kostov, P. Feulner, T.E. Madey, and D. Menzel, Chem. Phys. Letters 415 (2005) 165: “Stability of water monolayers on Ru(0001): Thermal and electronically induced dissociation”

  20. Some recent examples: Alkalis on the moon: “Far-out surface science“ Yakshinsky and Madey, Nature 400 (1999) 642 Water on Ru(0001): Faradzhev, Kostov, Feulner, Madey, Menzel, CPL 415 (2005) 165 Insensitivity of large conjugated p-systems to radiation damage: D. Menzel, P. Cloutier, L. Sanche, T.E. Madey, J. Phys. Chem. A 111 (2007) 12427: “Low-energy electron-induced damage in fluorinated copper phthalocyanine films, observed by F- desorption: Why so little damage ?” “The capacity of DNA to resist photodamage by rapidly dissipating the energy from ultraviolet light absorption is a key feature of long-term genetic stability. Many model studies have probed the underlying dynamics responsible for this dissipation, (Science 322, Oct.10,2008)“

  21. Some recent examples: Alkalis on the moon: “Far-out surface science“ Yakshinsky and Madey, Nature 400 (1999) 642 Water on Ru(0001): Faradzhev, Kostov, Feulner, Madey, Menzel, Chem. Phys. Letters 415 (2005) 165 Insensitivity of large conjugated p-systems to radiation damage: Menzel, Cloutier, Sanche, Madey, J. Phys. Chem. A 111 (2007) 12427 Nanostructures (facetted surfaces as structural selfassembly): T. E. Madey, W. Chen, H. Wang, P. Kaghazchi, T. Jacob, Chem. Soc. Rev. 37 (2008) 2310 DIET on metal nanoparticles: K. Watanabe, D. Menzel, N. Nilius, H.-J. Freund, in Photochemistry and Photophysics on Surfaces,Ed. J.T.Yates, Jr., Chem. Reviews 106 (2006) 4301; PRL 99(2007)225501 and 101 (2008) 146103.

  22. Thank you !

More Related