DIET: Changes and constants in

changing times.

Dietrich MenzelFritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin

and

Physik-Dept. E20, Techn. Univ. München, Garching (Germany)

In memoriam Ted Madey

Distinguished scientist

longtime Close friend

frequent collaborator

Early times:

1963

1973/74

Gomerfest May 1996

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

EID, ESD, DIET,

Surface photochemistry:

Coupling to surface also changes excited states and introduces possible charge and energy transfer:

Photochemistry changed Concentrate on first step: Breaking of bonds (dissociation, desorption)

Changes: MethodsMachines and radiation sources

The heroic times : 1962-1964

Paul Redhead,Can. J. Phys. 42, 886 (1964)

Today‘s uhv machinery: 10 cm 3 m

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

sources)

Constants in understanding:

Principles, mechanisms, and counteracting influences

Ene

rgy

Z

Ene

rgy

Z

-

Hot electron -TNI

DIET mechanisms

Direct

Ene

rgy

Z

Adsorbate or substrate mediated, depending on location of primary excitation

Localization vs. delocalization; steepness of potential

DIMET

h

Metal

Adsorbate

Fermi level

Vacuum level

h

Metal

Adsorbate

Fermi level

Vacuum level

Metal

Adsorbate

Vacuum level

hFermi level

Metal

Adsorbate

Vacuum level

hFermi level

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 decreases of 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 !!)

Adsorbates on metal and semiconductor surfaces

Explanation:Competition between

bond dissociation and

transfer of excitation (quenching by energy and/or

charge transfer):

LOCALISATION LOCALISATION

vs.

DELOCALISATIONDELOCALISATION

Observations:(For excitations by electrons or photons)

Compared to corresponding molecular processes: Considerably more neutrals than

ions (except high exc.) Strong decreases of 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 !!)

must be VERY fast !

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

Some early successes:

Isotope effectESDIADStrongly localising excitations (core, complex)

But not only DIET:

The ruthenium story: TPD, LEED, Auger, 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 Ow. John Fuggle, M. Steinkilberg (Phys. Lett. 51A (1975) 163; CPL 33 (1975) 233;

SS 52 (1975) 521)

Some early successes:

Isotope effectESDIADStrongly localising excitations (core, complex)

Some recent examples:

Alkalis on the moon: “Far-out surface science“

B. Yakshinsky and T.E. Madey, Nature 400 (1999) 642

Some recent examples:Alkalis on the moon: “Far-out surface science“

Yakshinsky and Madey, Nature 400 (1999) 642

Water on Ru(0001): Extreme radiation sensitivityN.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”

Some recent examples:Alkalis on the moon: “Far-out surface science“

Yakshinsky and Madey, Nature 400 (1999) 642

Insensitivity of large conjugated -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)“

Water on Ru(0001): Faradzhev, Kostov, Feulner, Madey, Menzel, CPL 415 (2005) 165

Some recent examples:Alkalis on the moon: “Far-out surface science“

Yakshinsky and Madey, Nature 400 (1999) 642

Insensitivity of large conjugated -systems to radiation damage: Menzel, Cloutier, Sanche, Madey, J. Phys. Chem. A 111 (2007) 12427

Water on Ru(0001): Faradzhev, Kostov, Feulner, Madey, Menzel, Chem. Phys. Letters 415 (2005) 165

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.

Thank you !