Theoretical Study of Coincident Ionization Cross-sections of Atoms and Molecules by Twisted Electron Impact

Abstract

The electron impact ionization process drives various physical processes. The geometry and kinematics of the (e, 2e) and (e, 3e) (single and double ionization) processes help one to study the dynamics of the collision process and also to probe the structure of the target atom, molecule, thin film, or surface. The generation of electron vortex (or twisted) beams (EVBs) has attracted much attention from both experimental and theoretical sides. In contrast to conventional (plane-wave) electron beams, twisted electron beams possess a nonzero projection of the orbital angular momentum (OAM) m onto their propagation direction. The intrinsic angular momentum of the electron vortex beam influences the role of the beam in the ionization process. To explore the influence of the kinematics of EVBs on the ionization processes, we theoretically studied the (e, 2e) and (e, 3e) processes on different atomic and molecular targets. We investigated the angular profiles of the triple differential cross-sections (TDCS) and five-fold differential cross-sections (FDCS) for different atomic and molecular targets for an incident twisted electron beam within the first Born approximation (FBA). We also present the average over-impact parameter cross-section ((TDCS)av) for the (e, 2e) processes. In the coplanar asymmetric geometry, we studied the twisted electron (e, 2e) process on noble gas atoms, H2, H2O, CH4, and NH3 molecules. We also investigated the angular profiles in the coplanar geometry for θ-variable and constant θ12 mode for the (e, 3e) process on the He atom. We examined the angular profiles of the TDCS for the atomic and molecular targets for the OAM number m and the opening angle θp of the twisted electron beam for the coplanar asymmetric geometry. The theoretical investigations on the different atomic and molecular targets revealed that the twisted electron parameters m and θp strongly influence the angular distribution of TDCS and FDCS in the given coplanar geometries.