Electron impact ionisation cross sections of iron hydrogen clusters

Abstract

Abstract: We computed electron impact ionisation cross sections (EICSs) of iron hydrogen clusters,FeHn with n =1,2,..,10, from the ionisation threshold to 10 keVusing the Deutsch-Märk (DM) and the binary-encounter-Bethe (BEB) formalisms. The maxima ofthe cross sections for the iron hydrogen clusters range from 6.13 × 10-16 cm2 at 60 eV to8.76 × 10-16 cm2 at 76 eV for BEB-AE (BEB methodbased on quantum-chemical data from all-electron basis sets) calculations, from4.15 × 10-16 cm2 at 77 eV to7.61 × 10-16 cm2 at 80 eV for BEB-ECP (BEBmethod based on quantum-chemical data from effective-core potentials for inner-coreelectrons) 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 onesobtained via the DM method, up to a factor of about two for FeH and FeH2. The formation of Fe-H bondsdepopulates the iron 4s orbital, causing significantly lower cross sectionsfor the small iron hydrides compared to atomic iron. Both the DM and BEB cross sectionscan be fitted perfectly against a simple expression used in modelling and simulation codesin the framework of nuclear fusion research. The energetics of the iron hydrogen clusterschange substantially when exact exchange is present in the density functional, while thecluster geometries do not depend on this choice. Graphical abstract: [Figure not available: see fulltext.]