Absolute total cross sections for electron-impact double ionization of He(1s2s 3S) and He−(1s2s2p 4P)★
Institute of Condensed Matter and Nanosciences, Université catholique de Louvain,
Louvain-la-Neuve 1348, Belgium
a e-mail: email@example.com
Received in final form: 11 December 2018
Published online: 7 February 2019
We report on the experimental determination of absolute, total cross sections for electron-impact double ionization of helium in its metastable 1s2s 3S state and of the helium negative ion He−(1s2s2p 4P). Cross sections are measured for impact energies ranging from threshold to 1000 eV using the animated crossed beams technique. The fast, pure beam of metastable helium required for the experiment is produced by photodetachment of fast He− ions. Results for He(1s2s 3S) are compared to those for He(1s2 1S), and exhibit similar magnitude and behaviour. The cross section for He− is large compared to other negative ions and indicates the predominance of indirect ionization channels at large impact energies.
© EDP Sciences / Società Italiana di Fisica / Springer-Verlag GmbH Germany, part of Springer Nature, 2019