Berlin 2014 – wissenschaftliches Programm
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MO: Fachverband Molekülphysik
MO 2: Clusters
MO 2.8: Vortrag
Montag, 17. März 2014, 12:15–12:30, BEBEL SR144
Surface Scattering of (CO2)n off Si(111)/SiO2 — Bo-Gaun Chen and •Wolfgang Christen — Humboldt-Universität zu Berlin, Brook-Taylor-Straße 2, 12489 Berlin, http://clusterlab.de
Employing a pulsed high-pressure supersonic jet expansion and a dedicated setup for the experimental investigation of chemical processes occurring between neutral, van der Waals bound clusters and a solid surface1, we report on the angular distribution of large CO2 clusters scattered off a Si(111)/SiO2 surface under ultrahigh vacuum conditions. Scattered particles are detected using time resolved mass spectrometry. A translator stage provides the possibility to sample both the incoming beam (target surface retracted) and to determine the angular and velocity distribution of scattered particles. Angular information is obtained by rotating the target surface, the velocity of scattered particles is determined by changing the distance between surface and mass spectrometer.
The presented studies cover a very broad range of cluster sizes, n, 5·103<n<2·105 molecules per particle, and focus on the influence of source entropy, realized by accurately setting stagnation pressure and temperature.
We observe an interesting dependence of the angular distribution of scattered CO2 monomers on source conditions, i.e. the scattering angle seems to reflect the expansion path, allowing to distinguish between cluster condensation via expansion on the gaseous or on the liquid side of the critical point, and an intermediate regime where the expansion passes the metastable gas-liquid region.
1 W. Christen, K. Rademann, Rev. Sci. Instrum. 77, 015109 (2006).