elektronimpactjonisering

Electron impact, sometimes written as elektron impact in non-English sources, refers to collisions between a beam of free electrons and atoms or molecules in a target. During such collisions, energy and momentum are transferred, leading to various outcomes depending on the incident energy and the target's structure.

The primary outcomes are ionization, where the target loses one or more electrons; excitation, in which the target is promoted to a higher electronic state without ionization; and dissociation or fragmentation, where chemical bonds break and molecular fragments are produced. Ionization requires surpassing the ionization energy of the target; excitation occurs at lower energies corresponding to electronic transitions; dissociation can occur at energies sufficient to overcome bond energies.

Cross sections quantify the probability of each process as a function of incident energy and target species. They typically rise from threshold, may peak, and then change with energy. At high energies, theoretical descriptions such as Bethe theory and the binary-encounter approximation are used, complemented by experimental measurements. Complex targets may exhibit multiple channels (single vs double ionization, various excited states) and interference effects.

Applications include electron ionization in mass spectrometry (EI-MS), which uses electron impact to ionize samples and generate characteristic fragmentation patterns; electron-energy-loss spectroscopy and other scattering methods in materials science; and modeling of plasmas and astrophysical environments where electron collisions drive ionization and excitation. The study of electron impact cross sections aids in understanding chemical processes, plasma processing, and the interpretation of emission spectra from astronomical sources.