- Photoionisation
Photoionisation is the physical process in which an incident
photon ejects one or moreelectrons from anatom ,ion ormolecule .The ejected electrons, known as
photoelectron s, carry information about their pre-ionised states. For example, a single electron can have akinetic energy equal to the energy of the incident photon minus theelectron binding energy of the state it left. Photons with energies less than the electron binding energy may be absorbed or scattered but will not photoionise the atom or ion.For example, to ionise
hydrogen , photons need an energy greater than 13.6electronvolt s, which corresponds to a wavelength of 91.2 nm [Carroll, B. W., Ostlie, D. A., (2007), "An Introduction to Modern Astrophysics", Wiley, p.121] . For photons with greater energy than this, the energy of the emitted photoelectron is given by::½"mv"2 = "hν" − 13.6 eV
where "h" is
Planck's constant and "ν" is thefrequency of the photon.Not every photon which encounters an atom or ion will photoionise it. The probability of photoionisation is related to the photoionisation cross-section, which depends on the energy of the photon and the target being considered. For photon energies below the ionisation threshold, the photoionisation cross-section is zero.
References
See also
*
Photoionization mode
*Electron binding energy
*Photoelectric effect
*Photoionization detector
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