Hannover 2003 – wissenschaftliches Programm
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A: Atomphysik
A 8: Atom–Atom/Molekülstöße
A 8.1: Vortrag
Dienstag, 25. März 2003, 11:00–11:15, F128
Quantum Effects in the Scattering Cross Section of 4He Dimers and Trimers. — •Oleg Kornilov, Rüdiger Brühl, Anton Kalinine, and J. Peter Toennies — Max-Planck-Institut für Strömungsforschung, Bunsenstr. 10, D-37073 Göttingen, Germany
The total scattering cross sections of the helium dimer (4He2) and trimer (4He3) scattered from krypton atoms are measured in the velocity range from 250 m/s to 800 m/s. The clusters are selected by diffraction from a 100 nm period transmission grating. The ratio of the dimer cross section to the He atom cross section is 2.0±0.1 independent of the collision velocity. For the trimer the ratio increases from 2.0 to 2.8 with velocity. Because of the large dimer bond distance (about 50 Å) the Kr atoms scatter impulsively from only one of the helium atoms explaining the factor of two. This model allows the Kr atoms to pass unhindered between the two He atoms. For the compact trimer (average radius 10 Å) a collective interaction model can explain the results. Since the trimer can only be in the ground rotational state its cross section is successfully simulated by distributing the three atoms uniformly on a spherical shell. The deviations from the model may be due to a small fraction of the long range excited Efimov state of 4He3 in the beam.