Charge transfer in low-energy collisions of H with He⁺and H⁺with He in excited states

Abstract

We present a theoretical study of charge transfer in collisions of excited (n = 2, 3) hydrogen atoms with He + and in collisions of excited (n = 2, 3) helium atoms with H +. A combination of a fully quantum-mechanical method and a semi-classical approach is employed to calculate the chargeexchange cross sections at collision energies from 0.1 eV/u up to 1 keV/u. These methods are based on accurate ab initio potential energy curves and non-adiabatic couplings for the molecular ion HeH +. Charge transfer can occur either in singlet or in triplet states, and the differences between the singlet and triplet spin manifolds are discussed. The dependence of the cross section on the quantum numbers n and l of the initial state is demonstrated. The isotope effect on the charge transfer cross sections, arising at low collision energy when H is substituted by D or T, is investigated. Finally, the impact of the present calculations on models of laboratory plasmas is discussed.

Evaluation of emission contributions from charge-exchange between the excited states of deuterium with He+ during diagnostic of thermal helium gas beam injection and laser-induced fluorescence

“…The excited deuterium (n = 2, 3)-He + CX crosssections for each of the two spin systems of helium have been recently calculated. 10 Including the channels for each of the spin systems is very important to take into account when modeling helium emission due to the long relaxation times of the metastable (See figure 1). In this work, only the cross-sections for deuterium were used since it is the main isotope used in AUG and in many other research reactors.…”

“…It was found that there are small isotopic differences in the cross-sections between hydrogen, deuterium, and tritium, particularly in the low collision energy region. 10 The cross-sections for both spin systems of helium are shown in figure 2.…”

“…Recent calculations have shown that there are isotopic differences in the cross-sections between; hydrogen, deuterium, and tritium, particularly at the lower limit of collision energies. 10 and m n is the mass of the neutrals, and γ = 5/3 for helium. 7,19 :…”

“…4,7 Recent atomic charge-exchange (CX) calculations from excited hydrogen isotopes with He + ions suggest that additional emission from recently formed helium neutrals may have to be taken into account in the lineratio calculation to obtain accurate electron densities and temperatures. 10 Excited hydrogen (n = 2, 3) with He + CX cross-sections are over 4-orders of magnitude higher than CX from the ground state (n = 1). [10][11][12] This CX process also occurs at lower energies where interactions between recently formed low temperature helium ions and hydrogen isotopes is more likely to occur, particularly in the edge and SOL regions.…”

“…10 Excited hydrogen (n = 2, 3) with He + CX cross-sections are over 4-orders of magnitude higher than CX from the ground state (n = 1). [10][11][12] This CX process also occurs at lower energies where interactions between recently formed low temperature helium ions and hydrogen isotopes is more likely to occur, particularly in the edge and SOL regions.…”