Dr. rer. nat. Wolfgang Christen

Profil

Zusammenfassung

Wolfgang Christen entwickelt experimentelle Methoden zur Erzeugung und Charakterisierung von hochdichten Molekularstrahlen und untersucht deren Wechselwirkungen mit Oberflächen. Seine Expertise umfasst die präzise Messung von Strahlparametern, die Untersuchung von Cluster-Oberflächen-Kollisionen und die Kontrolle von Kristallisationsprozessen unter extremen Bedingungen. Diese Kompetenzen sind relevant für Anwendungen in der Materialcharakterisierung, Oberflächenchemie und Präzisionsmessungen in der Molekularphysik.

Skills

Name

Dr. rer. nat. Wolfgang Christen

Titel

Dr. rer. nat.

Fakultät

Mathematisch-Naturwissenschaftliche Fakultät

Institut

Institut für Chemie

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HU-FIS-Profil

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28.6.2026, 01:04:12

• Bestimmung der Translationstemperatur bei der Hochdruck-Molekularstrahlexpansion kleiner Moleküle (I)

  Quelle ↗

  Förderer: DFG Sachbeihilfe Zeitraum: 07/2006 - 06/2007 Projektleitung: Dr. rer. nat. Wolfgang Christen

• Bestimmung der Translationstemperatur bei der Hochdruck-Molekularstrahlexpansion kleiner Moleküle (II)

  Quelle ↗

  Förderer: DFG Sachbeihilfe Zeitraum: 01/2008 - 06/2009 Projektleitung: Dr. rer. nat. Wolfgang Christen

• Erschließung von Zitationen in verteilten Open Access-Repositories

  Quelle ↗

  Förderer: DFG Sachbeihilfe Zeitraum: 03/2009 - 07/2013 Projektleitung: Dr. rer. nat. Wolfgang Christen

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• Generation and Propagation of Intense Supersonic Beams

  2011

  The Journal of Physical Chemistry A · 76 Zitationen · DOI

  Computer simulations and experiments have been performed to quantify the effects of nozzle shape and skimmer placement on high-density supersonic jets. It is shown that the on axis beam intensity achieved is much higher than intensity achieved using standard sonic nozzles. Changes in skimmer design and positioning are required to allow this intense jet to propagate in a typical supersonic beam setup.

• Cluster Impact Chemistry

  1998

  The Journal of Physical Chemistry A · 62 Zitationen · DOI

  This paper addresses the interaction of molecular cluster ions with a solid surface in the kinetic energy range of 1−100 eV/molecule. We report experimental results on the energy acquisition by the cluster following its impact on the target, the size distribution and the time scale of cluster fragmentation, and first examples of chemical reactions induced by cluster impact. In particular we show that for a p-type diamond film and moderate collision energies the elasticity of the cluster-surface impact is surprisingly high: The intact cluster recoils with typically 75% of its collision energy. Once, however, the clusters have acquired sufficient internal energy they will shatter, mostly to monomers. In the case of protonated ammonia cluster ions this shattering of clusters upon surface impact is shown to be faster than 80 ps. It provides evidence that the technique of cluster impact allows an ultrafast energy redistribution within superheated cluster ions prior to their fragmentation. The feasibility of this fascinating new approach to femtosecond chemistry is demonstrated with impact-induced chemical reactions of iodomethane clusters to molecular iodine and of trifluoromethane clusters to molecular fluorine. The detected reaction yields are surprisingly high, even for the small cluster sizes investigated so far (n < 16).

• Collisional energy loss in cluster surface impact: Experimental, model, and simulation studies of some relevant factors

  1998

  The Journal of Chemical Physics · 61 Zitationen · DOI

  Measurements of the collisional energy transfer of size and energy-selected ammonia cluster ions (NH3)nH+, n=1–10, impacting a silicon wafer coated with p-type diamond film are reported. The transfer from translational energy of the incident cluster ions to kinetic energy of intact scattered cluster ions has been studied as a function of impact energy, surface composition, and size of the impinging cluster cations. For low impact energies (&amp;lt;2.5 eV/molecule), cluster ions scattered off the target surface lost most of their initial kinetic energy, while for higher impact energies the elasticity of the cluster–surface collision is surprisingly high: Typically 75% of the impact kinetic energy is retained by the scattered parent clusters. Larger cluster ions are scattered less elastically and a large fraction of them shatter to small(est) fragments. The molecular dynamics simulations examine the two energy disposal regimes, deep inelasticity and shattering. Deep inelastic scattering occurs already below the lowest impact energies probed by the experiment. At higher collision energies, the energy loss continues to increase but a point is reached where most clusters shatter. Those few clusters that rebound intact have lost a disproportionately low fraction of their initial energy. The simulations also explore the cluster size effects, the role of the attraction to the surface, and the importance of the anisotropic forces between the molecules in the cluster. The experimental results and the simulations are discussed using the hard cube model with special reference to collective effects.

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