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Elementary Processes of Charged Species in Plasma
Published in Alexander Fridman, Lawrence A. Kennedy, Plasma Physics and Engineering, 2021
Alexander Fridman, Lawrence A. Kennedy
The first group, direct ionization by electron impact, includes the ionization of neural neutrals and preliminary not-excited atoms, radicals, or molecules by an electron, whose energy is sufficiently high enough to provide the ionization act in one collision. These processes are the most important in cold or nonthermal discharges, where electric fields and hence electron energies are quite high, but the level of excitation of neutral species is relatively moderate. The second group, stepwise ionization by electron impact, includes the ionization of preliminary excited neutral species. These processes are important mainly in thermal or energy-intense discharges when the ionization degree (ratio of number densities of electrons and neutrals) and the concentration of highly excited neutral species is quite high. The third group is the ionization by a collision of heavy particles. Such processes can take place during ion-molecular or ion-atomic collisions, as well as in collisions of electronically or vibrationally excited species when the total energy of the collision partners exceeds the ionization potential. The chemical energy of the colliding neutral species can be also contributed to ionization via the so-called associative ionization. The fourth group is the photoionization, where neutral collisions with photons result in the formation of an electron–ion pair. Photoionization is mainly important in thermal plasmas and some mechanisms of propagation of nonthermal discharges.
Hydrogen Photoionization with Strong Lasers
Published in Xavier Oriols, Jordi Mompart, Applied Bohmian Mechanics, 2019
Albert Benseny, Antonio Picón, Jordi Mompart, Luis Plaja, Luis Roso
In Einstein’s photoelectric effect [1], see Fig. 2.5a, ionization takes place by the absorption of a photon with an energy ħω0 larger than the ionization potential, IP, i.e., the minimum energy that the atomic electron has to acquire to reach the continuum. The remaining energy ħω0 − IP, is converted into kinetic energy for the ejected electron. From this point of view, the threshold photon frequency required to produce photoionization is ωth = IP/ħ.
The role of the intermediate state in angle-resolved photoelectron studies using (2 + 1) resonance-enhanced multiphoton ionization of the chiral terpenes, α-pinene and 3-carene
Published in Molecular Physics, 2021
Hassan Ganjitabar, Dhirendra P. Singh, Richard Chapman, Adrian Gardner, Russell S. Minns, Ivan Powis, Katharine L. Reid, Arno Vredenborg
For discussing MP-PECD measurements it is often convenient to define a Kuhn asymmetry factor [12] providing a single numerical measure of the chiral asymmetry of the photoelectron: where Ifwd and Iback are, respectively, the integrated electron count emitted into the forward and backward facing hemispheres, relative to the light propagation direction. The asymmetry, GAD, will, like the underlying photoionization dynamics, be dependent on the electron kinetic energy. It can be shown [13,14] that in terms of the angular distribution parameters Note that the sign of GAD will depend on specifying the polarization state p (or the subtraction order in Eq. (2)), but also the enantiomer. Switching enantiomer will cause all the terms appearing in Eq. (3) to change sign. By convention we will always specify these asymmetries for p = +1.
Anisotropic Stark effect of carbon monoxide: emergent orbital cooperativity
Published in Molecular Physics, 2020
Jibiao Li, Dian Wang, Xiaosong Zhu, Emeka Oguzie
Photoionization is another context where Stark effect finds an applicable ground in molecular interactions with strong laser fields. In contrast to HHG, photoelectrons containing the structural information of valence electrons are ejected to the infinite distance from the molecule. During the photoionization process, the photoelectrons experience the effect of electric fields. Stark effect takes effect in not only the ejected electron but also the whole valence electrons. Like HHG efficiency, the ionisation efficiency is highly dependent on the molecular orientations with respect to the electric field in the laser fields [41–43]. For the HOMO orbital, the most efficient ionisation occurs when the molecular axes are aligned along the electric fields, and the lowest ionisation efficiency appears for molecular axes set perpendicular to the electric fields. In other words, the parallel and perpendicular configurations would exhibit different Stark effects, which may help to gain insights into the nature of Stark effects when the molecular axes are set along and perpendicular to the electric fields.
Cascade production of secondary electrons and photons and energy absorption mechanisms in liquid nitrogen irradiated by photons in the energy range of 0.027–17.4 keV
Published in Radiation Effects and Defects in Solids, 2023
Alexander P. Chaynikov, Andrei G. Kochur, Victor A. Yavna
If the initial photon-atom interaction process is a single photoionization then a photoelectron with a certain energy and the direction of movement appears, and it is put on the monitoring list for further analysis. If an additional shake-off process happens then two electrons are born and put on the monitoring list. The ionic atomic state produced by the interaction with the incident photon is analyzed to see if its cascade decay is possible, and if so, a cascade simulation routine is activated. During the cascade development, cascade-produced electrons and photons are emitted and they are put on the monitoring list.