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@PHDTHESIS{Dederichs:28496,
      author       = {Dederichs, F.},
      title        = {{S}ummenfrequenz-{S}chwingungsspektroskopie an der
                      {P}latin/{F}lüssigkeit-{G}renzfläche},
      volume       = {3758},
      issn         = {0944-2952},
      school       = {Techn. Hochsch. Aachen},
      type         = {Dr. (FH)},
      address      = {Jülich},
      publisher    = {Forschungszentrum, Zentralbibliothek},
      reportid     = {PreJuSER-28496, Juel-3758},
      series       = {Berichte des Forschungszentrums Jülich},
      year         = {2000},
      note         = {Record converted from VDB: 12.11.2012; Aachen, Techn.
                      Hochsch., Diss., 2000},
      abstract     = {The last years have witnessed a tremendous advance in
                      understanding electrochemical interfaces. These insights
                      have been mode possible by the impmvement of existing and
                      the invention of new experimental techniques, respectively .
                      One of these methods is optical sumfrequency generation
                      (SFG), which in this work is applied to the investigation of
                      molecular vibrations at electrolyte/platinum interfaces . As
                      a second-order nonlinear optical effect, SFG is due to its
                      inherent interface sensitivity ideally suited for the
                      spectroscopy of electrochemical interfaces. In order to lay
                      the foundations for the experimental applications we start
                      with a theoretical description of sum-frequency generation
                      and discuss the experimental setup utilized in this work.
                      The first experimental chapter deals with the chemisorption
                      of carbon monoxide (CO) onto (111) and (110) platinum (Pt)
                      single-crystal faces in a CO-saturated 0 .1 M HC1O4 aqueous
                      electrolyte . Whereas CO adsorbs on Pt(110) only on terminal
                      sites as indicated by a single vibrational band around 2075
                      cmil in our sum-frequency spectra, we observe different
                      adsorption geometries on Pt(111) . For potentials below 0
                      .37 V/RHE CO adsorbs on terminal and hollow sites of the
                      (111) face while for higher potentials up to
                      electro-oxidation of the carbon monoxide at about 0 .55
                      V/RHE it occupies terminal and Bridge sites, respectively .
                      We discuss in detail the influence of the electrochemical
                      thin layer electrolyte in our spectrochernical cell on the
                      electro-oxidation of CO. We investigate the adsorption of
                      cyanide (CN) on Pt(111) surfaces by dissociation of
                      acetonitrile (CH 3CN) molecules from the vapor phase above
                      liquids containing acetonitrile, followed by irmnersion of
                      the sample into the liquid . Using optical sum-frequency
                      generation and cyclic voltammetry we can identify the
                      adsorbed Spezies unambiguously as cyanide by the
                      characteristic potential dependencies of the C-N stretching
                      vibration frequencies and the voltammetric profile in a (0.1
                      M HC1O4 + 25 M CH3CN) aqueous electrolyte . In neat
                      acetonitrile we observe two adsorbed states of CN with
                      vibrational bands at 1861 uni (hollow site) and 2073 cm-'
                      (on-top site), distinctly below and above that of the
                      isolated molecule, demonstrating a covalent CN-platinum bond
                      . We discuss duster calculations which show that the
                      weakening and strengthening of the C-N bond at the hollow
                      and on-top sites is due to a surface-induced depletion of
                      the Bonding In and antibonding 4o orbitals, respectively. In
                      the last poft of this work we present a sum-frequency study
                      of the electrochemical interface forrned by (111), (110) and
                      (100) platinum faces, respectively, with aqueous
                      electrolytes containing 0.1 M HCIO4. Despite of strong IR
                      absorption due to water molecules in the bulk electrolyte,
                      interfacial water vibrations are observed in our SFG spectra
                      because their bands are dramatically broadened towards lower
                      frequencies, containing components which are redshifted as
                      much as 1000 cri ' . We conclude that these frequency shifts
                      are caused by the strong, inhomogeneous eiearie field at the
                      electrochemical interface, which weakens the O- -bonds . A
                      detailed analysis of our sum-frequency spectra, using an
                      inhomogeneous broadened model function and taking into
                      account the linear-optical properties of the
                      three-layer-system CaF 2 (laser window)/aqueous
                      electrolyte/Pt electrode, allows us to deduce the potential
                      dependence of the SFG amplitude of the O-H-vibrations. Since
                      this amplitude of the water vibrations correlates with the
                      charge density on the platinum electrode surface, we are
                      able to estimate the potential of zero charge (PZC) of the
                      Pt electrodes . For Pt(111) in 0 .1 M HCIO4 we obtain a PZC
                      value of 0 .86 +20-.0128 V/RHE.},
      cin          = {IGV},
      cid          = {I:(DE-Juel1)VDB167},
      pnm          = {Struktur und Dynamik der Grenzflächen},
      pid          = {G:(DE-Juel1)FUEK261},
      typ          = {PUB:(DE-HGF)11 / PUB:(DE-HGF)3},
      url          = {https://juser.fz-juelich.de/record/28496},
}