Eur. Phys. J. D (2016) 70: 182
https://doi.org/10.1140/epjd/e2016-70292-4

Regular Article

Electron impact ionisation cross sections of iron hydrogen clusters^*

¹ Institute of Ion Physics and Applied Physics, University of Innsbruck, Technikerstraße 25, 6020 Innsbruck, Austria
² Department of Nuclear Physics and Biophysics, Faculty of Mathematics, Physics and Informatics, Comenius University, 84248 Bratislava, Slovakia
³ Department of Materials Science and Engineering, School of Molecular Science and Engineering, Vidyasirimedhi Institute of Science and Technology, Rayong 21210, Thailand

^a e-mail: michael.probst@uibk.ac.at

Received: 26 April 2016
Received in final form: 31 May 2016
Published online: 6 September 2016

Abstract

We computed electron impact ionisation cross sections (EICSs) of iron hydrogen clusters, FeH_n with n = 1,2,...,10, from the ionisation threshold to 10 keV using the Deutsch-Märk (DM) and the binary-encounter-Bethe (BEB) formalisms. The maxima of the cross sections for the iron hydrogen clusters range from 6.13 × 10^-16 cm² at 60 eV to 8.76 × 10^-16 cm² at 76 eV for BEB-AE (BEB method based on quantum-chemical data from all-electron basis sets) calculations, from 4.15 × 10^-16 cm² at 77 eV to 7.61 × 10^-16 cm² at 80 eV for BEB-ECP (BEB method based on quantum-chemical data from effective-core potentials for inner-core electrons) calculations and from 2.49 × 10^-16 cm² at 43.5 eV to 7.04 × 10^-16 cm² at 51 eV for the DM method. Cross sections calculated via the BEB method are substantially higher than the ones obtained via the DM method, up to a factor of about two for FeH and FeH₂. The formation of Fe-H bonds depopulates the iron 4s orbital, causing significantly lower cross sections for the small iron hydrides compared to atomic iron. Both the DM and BEB cross sections can be fitted perfectly against a simple expression used in modelling and simulation codes in the framework of nuclear fusion research. The energetics of the iron hydrogen clusters change substantially when exact exchange is present in the density functional, while the cluster geometries do not depend on this choice.