Direct Dissociative Excitation of Heteronuclear and Homonuclear Ions of Inert Gases by Electron Impact
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TROSCOPY AND PHYSICS OF ATOMS AND MOLECULES
Direct Dissociative Excitation of Heteronuclear and Homonuclear Ions of Inert Gases by Electron Impact K. S. Kislova, *, A. A. Naritsa, **, and V. S. Lebedeva, *** a
Lebedev Physical Institute, Russian Academy of Sciences, Moscow, 119991 Russia *e-mail: [email protected] **e-mail: [email protected] ***e-mail: [email protected] Received June 6, 2020; revised June 6, 2020; accepted July 28, 2020
Abstract—A theoretical description of the process of dissociative excitation of a molecular ion by an electron impact under the condition of effective population of a large number of its vibrational–rotational levels has been given. The approach is based on the quantum version of the theory of non-adiabatic transitions between electronic terms of a molecular ion and on the replacement of the summation with respect to v J -levels with the integration with respect to v and J . Semi-analytical formulas for the integral contribution of the entire vibrational–rotational quasicontinuum to the cross sections σTde (ε) and rate constants αde (T , Te ) of the process under study in a plasma with the Te and T temperatures of its electronic and ionic components have been obtained. The developed theory has been used to study the processes of dissociative excitation of heteronuclear (HeXe+ and ArXe+) and homonuclear (Ar2+ and Xe2+ ) ions of inert gases. A strong dependence of the results on the ion dissociation energy and large differences in the behavior and characteristic values of σTde (ε) and αde (T , Te ) for these systems in different energy, ε , and temperatures, Te and T , has been established. The regions of dominance of the contributions of two competing channels: direct dissociative excitation and dissociative recombination to the total cross sections and the rate of destruction of molecular ions of inert gases by electron impact have been determined. The analysis of the behavior of the differential rate constants of dissociative excitation in a unit electron energy interval in the final reaction channel has demonstrated qualitative differences in the dynamics of this process in the cases of weakly and moderately bound molecular ions. Keywords: dissociative excitation, collisions with electrons, dissociative recombination, non-adiabatic transitions, electronic terms, homonuclear and heteronuclear ions of inert gases DOI: 10.1134/S0030400X20110144
1. INTRODUCTION The processes of formation and breakup of molecular ions are of interest for spectroscopy, kinetics and diagnostics of low-temperature plasma [1–3], physics of stellar and planetary atmospheres [4–6], physics of the early universe [7, 8], and the development of sources of VUV radiation [9] and high-power gas lasers [10–13]. Much attention is paid, in particular, to the study of the processes of collision of molecular ions with electrons, including ionization [14], fragmentation [15, 16], dissociative recombination [17], and direct dissociation by electron impact [18, 19]. One of the most effective mechanisms of molec
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