Electron ionization doubly charged ions

Doubly-charged ions exist because the potential of second ionization of many metals is relatively low with respect to the plasma thermal energy. For instance, 11.9 eV are needed to remove two electrons, in contrast with 6.1 eV for one electron, from a calcium atom. At 8000K, a little less than 0.1% of Ca would be in the Ca + form and overlap with Mg+ isotopes. Likewise, Ba is rather easily formed and overlaps with Zn+ isotopes. Isobaric interferences with doubly-charged ions are easily identified as odd-mass atoms will produce peaks at half masses, such as Ca at mass 21.5. 

While the doubly charged ion, is an even-electron ion, the triply charged ion, again is an odd-electron ion. In addition, there are several other events possible from the electron-neutral interaction, e.g., a less effective interaction will bring the neutral into an electronically excited state without ionizing it. 

The future of this field clearly will rely on extending these, or some other, methods to study two-electron systems and simple molecular systems. There is evidence that electron-electron correlation continues to play a role in excitation dynamics even in very intense fields. The interaction can be small, but it has been observed to yield orders of magnitude enhancements in the production of doubly charged ions for intensities below that at which sequential ionization becomes efficient. In molecules, the transfer of absorbed energy from the electrons to the nuclei which controls the competition between ionization and dissociation is another important and developing field of research. 

Another unusual type of highly excited doubly charged ion has one hole in a deep inner shell and one in the valence shell. Such states are of interest theoretically because of (a) the presence of distinct electron vacancies and (b) several possible pathways for their production [86]. The first observation of direct formation of such states in Ne and N2 was recently achieved by the magnetic bottle TOF method [87]. The cross section for their formation is very low, and the electron distribution in the Ne case shows both a direct contribution and an indirect pathway. For the final states from s l2p l ionization the intermediate states are satellites of the Islsi1 3S)ns series whose lines show asymmetric Fano profiles. The presence of these profiles demonstrates that the matrix elements representing direct double ionization, formation of the intermediate states, and interaction of those states with the continuum are of similar magnitudes. 

The ionization constant, KIf is assumed to be independent of the gas concentration, though it will vary with gas species. Other effects can occur during electron bombardment. These include dissociation and recombination phenomena along with the production of doubly charged ions. 

It gives a measure of the ability of metals to form positive ions. The second ionization potential is the energy required to remove two electrons and form a doubly charged ion ... 

During the last few years, a comprehensive set of experimental data has been obtained for the double ionization of atoms for impact of charged particles like electrons, protons and heavy ions, as well as for positrons and antiprotons. It has been possible to obtain such data because the created, doubly charged ions are easily collected and detected with high efficiency. This compensates for the very small intensity of available antiparticle beams. In the following, we shall discuss the various mechanisms that lead to double ionization of atoms (or molecules) by impact of fast, charged particles, but clearly the same mechanisms may as well lead to excitation plus ionization or to double excitation. 

One form of selective reaction between an unwanted ion and the reaction gas molecules is electron transfer. Spontaneous electron transfer from a reaction gas molecule to an ion occurs when the ionization energy of the former is lower than that of the neutral entity at the basis of the interfering ion (first ionization energy in the case of a singly charged ion, second in the case of a doubly charged ion). A few examples of this approach are presented below. 

We disccunt the electrostatic lens effect occurring in the acceleration zone of the thruster channel, causing the divergence of the jet. The ionization reaction is Xe + e Xe + e + e. The energy of the electrons creates few doubly-charged ions. 

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