Osnabrück 2002 – wissenschaftliches Programm
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A: Atomphysik
A 2: Cluster I: Moleküle und Atome in Heliumclustern (gemeinsam mit FV Molekülphysik)
A 2.1: Vortrag
Montag, 4. März 2002, 16:30–16:45, HS 01/E01
The formation of small clusters in free jet 4He expansions. — •Oleg Kornilov1, Rüdiger Brühl1, Wieland Schöllkopf2, and Peter Toennies1 — 1Max-Planck-Institut für Strömungsforschung, Göttingen — 2Harvard University, Lyman Lab, Cambridge, MA 02138
The formation of small van der Waals helium clusters with less than n=13 atoms produced in a free jet expansion was investigated by measuring the intensity of each individual cluster by diffraction from a transmission grating with 100 nm period. The mole-fractions of the different clusters for source temperatures of 30, 12 and 6 K were measured in the range of source pressures from 0.1 to 80 bar. With increasing pressure the mole-fractions for each n pass through a maximum and almost disappear above a certain source pressure. At each temperature there was a distinct pressure before clusters n ≥ 13 appeared. At higher pressures the avalanche-like formation of larger clusters suggests that the n=13 clusters are the critical clusters in the standard theory of homogeneous nucleation.