Electron capture and excitation in slow H⁺+ He*(n= 3) collisions

Abstract

The electron-capture and excitation processes in slow collisions of protons with He * (1s3l) are studied using the close-coupling method within the semiclassical approximation. The Stark splitting of electron-capture states on H is explicitly taken into account and the coupling-matrix elements between these states and the initial angular-momentum states on He are calculated analytically. The cross sections for excitation (de-excitation) and single-electron capture to specific spherical hydrogen states have been calculated in the relative velocity range 2 × 10 6 -1.3 × 10 8 cm s −1 . The cross section values for both types of processes in the considered velocity range are found to be large (10 −14 -10 −13 cm 2 ) due to the large values of electron-exchange couplings at large internuclear distances. The excitation (de-excitation) processes are controlled by two-step exchange (capture and re-capture) transitions rather than by direct coupling among the states centred on He.

Ab initiocalculation ofH+He+charge-transfer cross sections for plasma physics

“…The dissociative atomic states and the asymptotic energies of the molecular states are shown in table I. We have also considered the n = 2 3 Σ + and 3 Π states to allow the comparison with [18,19] (see section 3.6). The adiabatic potential energy curves (PEC) for these states have been calculated using the ab initio quantum chemistry package MOLPRO version 2006.1 [22].…”

“…and neglecting electron translational factors and rotational couplings [18,19]. These works provide data for an energy range between 2.5 eV/amu and 10 keV/amu.…”

Proton impact charge exchange and excitation cross sections for liquid Sn divertor studies

“…The strength of the matrix elements is proportional to the overlap <k | l> of the wave functions of coupled states |k >, |l > , and therefore, H ii , H jj are localized dominantly near the pertinent atom, while K ij , K ji are distributed on the internuclear axis at distances relatively far from the atoms. [2,16] Figure 1 but for capture to 2l states of H In Figures 1-5, we show the cross sections for electron capture from the singlet (panels [a]) and triplet (panels [b]) initial Sn(5 2 5 21,3 ) and the total (c), Equation (10), to the 1s states and 2l, 3l, 4l, and 5l states of hydrogen atom. When the states |k >, |l > belong to different atomic centres, the condition E k = E l ensures a strong (resonant) coupling between the states.…”

“…The electron exchange between these pairs of energetically quasi-resonant states is very effective and represents one of the major mechanisms distributing the probability flux between the electron capture and excitation channels at low collision energies. [2,16] Figure 1 but for capture to 2l states of H In Figures 1-5, we show the cross sections for electron capture from the singlet (panels [a]) and triplet (panels [b]) initial Sn(5 2 5 21,3 ) and the total (c), Equation (10), to the 1s states and 2l, 3l, 4l, and 5l states of hydrogen atom. We note that, at the higher energies (E > 30 − 40keV), the electron capture process is governed mainly by the reaction energy defect and the electron momentum transfer mechanism, [2] while at energies below ∼10 − 15keV, interstate couplings determine its dynamics, producing secondary maxima and even oscillatory behaviour of the cross sections (cf., e.g.…”

“…However, in the energy region below approximately 10keV, where the coupling between the excitation and electron capture channels is strong (especially for the quasi-resonant states), significant contribution to their population may come from the back-capture process. [16] The energetically quasi-resonant Sn(5pnl) and H(n ′ ) states are listed in Table 5. This capture-excitation mechanism is responsible not only for the increase of the excitation cross sections when collision energy decreases below approximately 10 keV but also for the appearance of additional maxima observed in all excitation cross sections in this energy region, as well as for the oscillatory structures in the cross sections (cf.…”