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Ionization of an atom in a collision with a resonantly excited atom

Ionization of an atom at a collision with a resonantly excited atom

A* + B -> A + B+ + e                                                            (1)

plays an important role in the balance of charged particles and resonantly excited atoms in weakly ionized gases containing as an admixture atoms with low ionization potential (comparing to that of the resonantly excited gas). As examples of such systems can be mentioned the active media of some gaseous lasers and luminescence lighting lamps, photoresonant plasma formed under the action of resonant irradiation onto a gas, plasma of MHD generators etc.

At a laboratory temperature (T < 1 eV) the process (1) proceeds effectively if the excitation potential of a resonantly excited atom A* exceeds the ionization potential of atom B. Under this condition the cross section of the process (1) is calculated within the frame of asymptotic method taking into account a large magnitude of the cross section comparing to the characteristic atomic size. Therefore the ionization occurs predominantly at large distance between the colliding atoms where the inter-atomic potential is well described by a long range interaction. The ionization in considered as the photo-ionization of atom B by the resonant photon emitted by the excited atom A*. The cross section of the process (1) is represented through the parameters of the resonantly excited state and the cross section of photo-ionization of atom B. The accuracy of calculation is determined by the uncertainty of reference data on the photo-ionization cross section. Table 1 compares the magnitudes of the cross section of process (1) calculated for A = He(3P) and B = Ne, Ar, Kr, Xe at the collision energy E = 0.05 eV with those measured in [1].


Table 1. The cross section of the process He* + B ->He + B+ + e at E = 0.05 eV calculated by KINTECH Lab and measured in [1] (Å2)
  Ne Ar Kr Xe
Calculation 20 40 39 56
Measurement [1] 28 ± 4 56 ± 10 50 ± 8 73 ± 12

[1]. S. Kubota, C. Davies and T.A. King J. Phys. B. 8 1220 (1975)

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