Elektronimpakti

Elektronimpakti is a process in which a free electron collides with a target particle, typically an atom or molecule, and transfers energy through the Coulomb interaction. If the collision is inelastic, the internal energy of the target changes, leading to electronic excitation, ionization, or dissociation, while elastic collisions leave internal states unchanged.

In atomic targets, the main inelastic channels are electronic excitation and ionization; in molecular targets, excitation, ionization, and fragmentation into fragments are possible. The collision energy must exceed the relevant threshold: the excitation energy, the ionization energy, or the dissociation energy.

The probability of a given outcome is described by a cross section, which depends on the incident electron energy and sometimes on the scattering angle. Ionization cross sections typically rise sharply just above the ionization threshold and may peak at moderate energies before decreasing at higher energies. Theoretical treatments include quantum-mechanical scattering theory; the Bethe (or Born) approximation for high-energy ionization and Mott theory for elastic scattering; various semi-empirical formulations and classically inspired models such as the binary-encounter model.

Applications of electron impact processes are widespread. In mass spectrometry, electron ionization (EI) is used to ionize and fragment molecules for analysis. In electron microscopy and spectroscopy, elastic and inelastic collisions provide contrast and spectroscopic signals. Electron-impact data underpin plasma physics, lighting technologies, and the modeling of planetary and interstellar atmospheres.

Historically, measurements of electron impact ionization and excitation began in the early 20th century and helped establish quantum collision theory. Today, experimental data and theoretical calculations are organized in cross-section databases that support research in chemistry, physics, and materials science.