Related Experiment Video
Updated: Aug 11, 2026

Photoelectron Imaging of Anions Illustrated by 310 Nm Detachment of F−
Published on: July 27, 2018
Electron-impact ionization of helium clusters close to the threshold: appearance energies
S Denifl1, M Stano, A Stamatovic
1Institut für Ionenphysik, Leopold Franzens Universität, Technikerstrasse 25, A-6020 Innsbruck, Austria.
Abstract:
We have investigated the ionization threshold behavior of small helium cluster ions (cluster size n=2-10) formed via electron-impact ionization of neutral helium droplets and derive appearance energies for mass-selected cluster ions using a nonlinear least-square-fitting procedure. Moreover, we report magic numbers in the mass spectrum observed at the electron energy of 70 eV. The apparatus used for the present measurements is a hemispherical electron monochromator combined with a quadrupole mass spectrometer. Our experiment demonstrates that helium clusters are not only exclusively formed via direct ionization above the atomic ionization potential but also indirectly via autoionizing Rydberg states. The present results are compared with previous electron-impact and photoionization results.
Related Concept Videos
Chemical Ionization (CI) Mass Spectrometry
Ionization Energy
Mass Spectrometry: Alkyl Halide Fragmentation
Nuclear Binding Energy
Mass Spectrometry: Molecular Fragmentation Overview
One type of fragmentation pattern is the cleavage of a single bond in the molecular ion. The cleavage leads to a radical and a cation. The cleavage can occur at...
The Energies of Atomic Orbitals

