Direct dissociative excitation of heteronuclear and homonuclear rare-gas ions by electron impact

A theoretical description of the process of dissociative excitation of a molecular ion by electron impact in the case of effective population of a huge number of its vibrational-rotational levels is presented. Our consideration is based on the quantal version of the theory of non-adiabatic transitions between the electronic terms of a molecular ion combined with replacing the summation over $vJ$-levels by integration over $v$ and $J$. Semianalytical formulas are derived for the integral contribution of the entire vibrational-rotational quasicontinuum to the cross sections, $\sigma_T^{\mathrm{de}}(\varepsilon)$, and the rate constants, $\alpha^{\mathrm{de}}(T, T_e)$ of the process under study in a plasma with temperatures $T_e$ and $T$ of its electronic and ionic components. The developed theory is used to study the processes of dissociative excitation of heteronuclear (HeXe$^{+}$ and ArXe$^{+}$) and homonuclear (Ar$_2^{+}$ and Xe$_2^{+}$) ions of inert gases. We demonstrate a strong dependence of the results on the ion dissociation energy and large differences in the behavior and characteristic values of $\sigma_T^{\mathrm{de}}(\varepsilon)$ and $\alpha^{\mathrm{de}}(T, T_e)$ for these systems in different ranges of electron energy, $\varepsilon$, and temperatures $T_e$ and $T$. The regions of dominance of the contributions of two competing channels are determined: direct dissociative excitation and dissociative recombination into total cross sections and the rate constants of destruction of rare gas molecular ions by electron impact. Analyzing behavior of the differential rate constants of dissociative excitation per unit range of electron energy in the final channel of reaction we demonstrate qualitative differences in the dynamics of this process for weakly bound and moderately bound molecular ions.