Berlin 2001 – wissenschaftliches Programm

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A: Atomphysik

A 13: Photoionisation I (joint session A and MO)

A 13.10: Vortrag

Donnerstag, 5. April 2001, 18:00–18:15, H1012

Helium Photodouble Ionisation-Towards Full Parametrisation of the Triple Differential Cross Section — •S. Cvejanovic and U. Becker — Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin, Germany

The study of the angular and energy distribution (TDCS) of the two released electrons in the photodouble ionisation (PDI) of helium has become a test ground for the role of electron correlations. While both the initial-state and the final-state correlations are important, at not too high excess energy the Coulomb interaction between the three particles during the escape stage is dominant. A simple quantification of the dynamic aspect of the TDCS became possible through a general parametrisation formula (1) with specific model functions for the mutual angle dependence of the two constituent transition amplitudes (splitting due to wave-function symmetry). Recent extension (2) of the near-threshold model to the intermediate energy range (E 50 eV) and an arbitrary energy sharing requires only three empirical parameters - the "correlation width" Γ(E), the ratio between the ungerade and the gerade amplitude η(E₁, E₂) and the phase difference between them φ(E₁, E₂). In this report we propose a full dynamic parametrisation of the helium TDCS within the above model by expressing all amplitude parameters via the energies of the two electrons. This empirical parametrisation is consistent with the existing data corpus, including unpublished TOF measurements at E = 20 eV, and possesses the required behaviour at the dynamic limits.

[1] A. Huetz et al (1991) J. Phys. B 24 191

[2] S. Cvejanovic and T. J. Reddish (2000) J. Phys. B 33 4691