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The ejection of one or more electrons from an atom, molecule, or positive ion following the absorption of one or more photons. The process of electron ejection from matter following the absorption of electromagnetic radiation has been under investigation for over a century. The earliest measurements involved the ultraviolet irradiation of metal surfaces. The theoretical interpretation of this phenomenon, known as the photoelectric effect, played an important role in establishing quantum mechanics. It was shown that, contrary to classical ideas, energy exchanges between radiation and matter are mediated by integral numbers of photons. In the gas phase the photoeffect is called either photoionization (atoms, molecules, and their positive ions) or photodetachment (atomic and molecular negative ions). See Photoemission

Photoionization involves a radiative bound-free transition from an initial state consisting of n photons and an atom, molecule, or ion in a bound state to a final continuum state consisting of a residual ion (or an atom in the case of photodetachment) and m free electrons; that is,

In the simplest atomic photoionization process a single electron is ejected from an atom following the absorption of a single photon. Each mode of fragmentation defines a final-state channel that is characterized by the energy and angular momentum of the outgoing electron as well as the excitation state of the residual ion. Since the photoionization process is endoergic, each channel has a well-defined threshold energy below which the channel is energetically closed. The threshold photon energy for a particular channel is equal to the binding energy of the electron that is to be ejected plus the excitation energy, if any, of the residual ion.

Above threshold, the energy carried off by the outgoing electron represents the balance between the energy supplied by the photon and the binding energy of the electron plus the excitation energy of the residual ion (neglecting the small recoil of the heavy ion). A photoelectron spectrum is characterized by a discrete set of peaks, each peak being associated with a particular state of the residual ion. Information on the excitation state of the ion following photoionization can also be obtained by monitoring the fluorescence emitted in the subsequent radiative decay of the state. One of the earliest applications of photoionization measurements was the investigation of the structure of atoms by determining the binding energies of both outer- and inner-shell electrons by means of photoelectron spectroscopy. See Atomic structure and spectra

McGraw-Hill Concise Encyclopedia of Physics. © 2002 by The McGraw-Hill Companies, Inc.


(foh-toh-ÿ-ŏ-ni-zay -shŏn) The ionization of an atom or molecule by photons of electromagnetic radiation. A photon can only remove an electron if the photon energy exceeds the first ionization potential of the atom or molecule. The excess energy is shared between the electron and the ion so that the electron can leave the atom with considerable velocity. If the radiation is of sufficiently high energy more strongly bound electrons will be removed, leaving the resulting ion in an excited state. See also recombination line emission.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006


(physical chemistry)
The removal of one or more electrons from an atom or molecule by absorption of a photon of visible or ultraviolet light. Also known as atomic photoelectric effect.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Global VOC Gas Meter Product Types In-Depth: PID (Photoionization Detector), Metal-oxide Semiconductor
Photoionization cross sections of the fullerenes C2o and Ca0 calculated in a simple spherical model.
Steroid profiles using liquid chromatography-tandem mass spectrometry with atmospheric pressure photoionization source.
For this purpose, is required a combination of high resolution and sensitivity given by different detectors such as photoionization (UV), infrared (IR), or photodiodes (DAD).
Barcelo, "On-line solid phase extraction-liquid chromatography-tandem mass spectrometry for insect repellent residue analysis in surface waters using atmospheric pressure photoionization," Journal of Chromatography A, vol.
This work focuses on finding the thermal and time evolution parameters of MIC in the interfacial system [alpha]-Si/Sn, evaluating the role of photoionization processes in Si nanocrystallites formation, and exploring possible advantages of employing a pulsed laser radiation to control the nanocrystals' size and partial volume during Sn-induced crystallization of [alpha]-Si.
Moreover, ionization mass spectrometry techniques such as direct analysis in real time (DART), desorption electrospray ionization (DESI), low-temperature plasma (LTP), desorption atmospheric-pressure photoionization (DAPPI), paper spray (PS), touch spray mass spectrometry (TS-MS), more recently in toxicological analysis laser diode thermal desorption (LDTD), and atmospheric solids analysis probe (ASAP) have gained popularity as they can be used with less or even without sample preparation [8-10].
Carter, "The determination of molecular properties from MULTIMODE with an application to the calculation of Franck-Condon factors for photoionization of C[F.sub.3] to C[F.sub.3.sup.+]," Molecular Physics, vol.
where A corresponds to the spectrum area after Shirley background subtraction and normalization to the background level, T is the relative transmission function of the X-24A analyzer [41], [sigma] is the Scofield photoionization cross section [42], X is defined as above, and the summation index j runs over all distinct elements analyzed.
There are several methods to generate plasma, including gas discharge, photoionization, heat radiation, and radio frequencies.