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O: Oberflächenphysik
O 11: Grenzfl
äche fest-flüssig
O 11.2: Vortrag
Montag, 24. März 2003, 15:15–15:30, M\"UL/ELCH
Surface segregation in liquid water probed by photoemission — •Ramona Weber1, Bernd Winter1, Cynthia Heiner1, Philipp Schmidt1, Wolf Widdra1,2 und Manfred Faubel3 — 1Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max-Born-Str. 2A, 12489 Berlin, Germany — 2Institut für Atomare Physik und Fachdidactik, Technische Universität Berlin, Germany — 3Max-Planck-Institut für Strömungsforschung, Bunsenstr. 10, 37073 Göttingen, Germany
Application of photoelectron spectroscopy to investigate liquid water surfaces is achieved by using a 6 µm liquid jet. Photoemission spectra were measured for various salt concentrations of aqueous alkali halides and of hydrophobic tetrabutylammoniumiodide (TBAI). The experiments were performed at the MBI-BESSY beamline in the 40 - 120 eV photon energy range. Whereas the surface segregation of the TBA+ cations in TBAI aqueous solutions is expected, we also observed surface segregation of the I− anions. The completion of a surface dipole monolayer as a function of salt (TBAI) concentration can be directly identified in the spectra. The behavior resembles the specific attenuation of substrate signal characteristic for adsorbate systems growing layer-by-layer. For the non-surface active salt, NaI, the nonlinear intensity increase as a function of the salt concentration points to a relative depletion of both solvated anions and cations in the near-surface region. Surface ion exchanges for mixed (TBAI and alkali halides) solutions show the reluctance of the larger I− anions to exchange with the smaller Br− anions.