Fotoniionisaatiolla

Fotoniionisaatiolla, or photoionization in English, is a physical process where an atom or molecule absorbs one or more photons and loses one or more electrons. This results in the formation of a positively charged ion and one or more free electrons. The energy of the absorbed photons must be sufficient to overcome the binding energy of the electron, also known as the ionization potential.

This phenomenon is fundamental to many areas of physics and chemistry. In astrophysics, photoionization plays a crucial role in the formation and evolution of nebulae and stellar atmospheres. The intense ultraviolet radiation emitted by stars ionizes the surrounding gas, creating glowing clouds of plasma. In atmospheric science, photoionization of atmospheric gases by solar ultraviolet and X-ray radiation is responsible for the creation of the ionosphere, a region of Earth's upper atmosphere that affects radio wave propagation.

In laboratory settings, photoionization is utilized in various spectroscopic techniques, such as photoelectron spectroscopy, to probe the electronic structure of atoms and molecules. It is also a key process in the operation of certain types of detectors and in plasma generation for research and industrial applications. The energy threshold for photoionization depends on the specific element or molecule and the electron being removed. Higher energy photons are required to ionize inner-shell electrons compared to outer-shell electrons.