Photoionization phenomena near the double-ionization threshold of helium
- 1 January 1991
- journal article
- Published by IOP Publishing in Journal of Physics B: Atomic, Molecular and Optical Physics
- Vol. 24 (1) , 115-125
- https://doi.org/10.1088/0953-4075/24/1/014
Abstract
A sensitive electron spectrometer has been used to study photoionization processes in the region of the double-ionization threshold of helium. Analysis of the cusp observed at the He2+ potential in a threshold photoelectron spectrum indicates that this structure would support the predictions of Wannier theory with a range of validity of 2.0+or-0.5 eV. Asymmetry parameters ( beta ) have been obtained for near-threshold excitation of He+ *(n) satellite states up to and above n=10 at photoelectron energies of 0.14 and 0.25 eV. For n)6, beta was found to have a roughly constant value of about -0.5 and did not approach the predicted value of -1. Similarly, for the double-ionization process, beta is approximately constant at -0.4 in the energy range from 0.25 to 2.0 eV above the He2+ potential and does not display the steep rise from beta =-1 to positive values which is predicted to occur in this energy range.Keywords
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