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MO: Molekülphysik

MO 3: Cluster I: Moleküle und Atome in Heliumclustern (gemeinsam mit FV Atomphysik)

MO 3.1: 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.