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Studies of radiative transitions between ground and charge transfer excited terms of heteronuclear rare-gas (ArXe)+ and (KrXe)+ ions with small and moderate dissociation energies ( D 0 ArXe + = 179 and D 0 KrXe + = 389 meV) are reported. Potential energy curves and dipole transition matrix elements are evaluated using ab initio calculations based on the CASSCF method followed by the NEVPT2 treatment and perturbative description of relativistic effects as implemented in the ORCA suite. We develop an efficient approach for the calculations of Boltzmann-averaged cross sections, rate constants, and absorption and emission coefficients associated with the integral contributions of bound–bound and bound–free transitions from a manifold of rovibrational states of the (RgXe)+ ion. A similar approach is used for the description of the free–free and free–bound transitions between different electronic terms of a quasimolecular (RgXe)+ ion temporarily formed during a collision of Ar or Kr atoms with Xe+ ions. Our method is based on the quantal version of the theory of non-adiabatic transitions in molecular and quasimolecular systems combined with the approximation of a quasicontinuum for rovibrational energy levels. This allowed us to obtain a semianalytic expression for the integral absorption properties particularly relevant at elevated temperatures. We perform a comprehensive analysis of the identified radiative processes in local thermodynamic equilibrium plasmas of rare gas Rg/Xe mixtures containing both atomic, Xe+, and molecular, RgXe+, ions and determine their role in the formation of the absorption and emission spectra in a wide range of wavelengths and gas temperatures. The results obtained are in good agreement with the available experimental data. [ABSTRACT FROM AUTHOR]

We have developed a semiclassical approach to the description of resonant dissociative excitation of a molecular ion induced by collisions with plasma free electrons and accompanied by the non-adiabatic transitions between its different electronic terms. It is based on the quasistatic treatment of nuclear particles relative motion in a molecular ion combined with the approximation of a quasicontinuum for rovibrational states. We have derived the semianalytic expressions for the Boltzmann-averaged cross sections, , and rate constants, αde(T, Te), of this process. The resulting expressions for and αde(T, Te) with explicit dependencies on the electron energy, ɛ, the gas, T, and electron, Te, temperatures are valid when the thermal energy kBT exceeds the value of the lowest vibrational quantum, ℏωe, of a molecular ion. The theory developed is applied to studying the resonant dissociative excitation of homo-nuclear , and ions as well as the hetero-nuclear rare gas ions RgXe+ (Rg = Ne, Ar, and Kr) with significantly different values of the dissociation energy. The efficiencies of the electron-impact dissociative excitation process and dissociative recombination leading to the population of the Rydberg states are compared. Our results of calculations are in good agreement with the available experimental data. [ABSTRACT FROM AUTHOR]

We study various physical mechanisms of electron-ion recombination accompanied by the formation of Rydberg atoms in plasmas containing atomic and molecular ions. Analytical approach to the description of resonant mechanism of ternary electron capture associated with the non-adiabatic energy transfer from free electron to the electronic shell of a quasimolecular ion is developed. Similar technique is used for the evaluation of the integral contribution of all rovibrational states of a bound molecular ion to the Boltzmann-averaged cross section and rate constant of dissociative recombination (DR). Simple expressions for cross sections and rate constants of non-resonant electron capture to Rydberg states in ternary electron-ion-atom collisions are derived in the impulse approximation. We perform a comparative analysis of the efficiencies of resonant and non-resonant three-body recombination of electrons with atomic ions and DR of molecular ions in plasmas of rare gas mixtures, Rg/Xe, with small relative concentration of xenon ([Xe] ≪ [Rg], Rg = He, Ne, Ar, Kr). It is shown that in a wide range of plasma parameters the resonant recombination mechanisms are predominant. The behavior and magnitudes of the recombination rate constants turn out to be quite different for heteronuclear ions with small (HeXe+ and NeXe+, D0 = 13.1 and 33 meV) and moderate (ArXe+ and KrXe+, D0 = 171 and 400 meV) values of the dissociation energy. [ABSTRACT FROM AUTHOR]

The effect of free-bound and bound-bound resonance nonadiabatic transitions of an electron on electron-ion recombination rates in the plasma of a Ne/Xe and Ar/Xe inert gas mixture has been studied. A kinetic model of recombination has been proposed including energy relaxation in collisions with electrons, resonant electron capture to Rydberg states through three-body collisions of Xe+ ions with Ne or Ar atoms and dissociative recombination of NeXe+ or ArXe+ ions, and n → n' resonance transitions. It has been shown that effective resonance processes occurring in quasimolecular systems sharply increase both the recombination coefficient and the effect of collisions with neutral particles even at quite high degrees of ionization of the plasma. [ABSTRACT FROM AUTHOR]