State-selective electron capture following - Li collisions for impact energies from 0.1 to

Abstract

The effect of the velocity of the incident ions in the n -distributions for n = 8 and 9 of the electron capture in collisions of highly charged Ar 8+ ions with a lithium target is studied in the 0.1-1 keV amu −1 energy range. The experimental n -distributions are deduced from the measured emission cross sections of all lines corresponding to 7 -8 and 8 -9 transitions. The results of theoretical calculations using the three-body classical trajectory Monte Carlo (CTMC) method are presented for the Ar 8+ -Li(2s) system and also for the O 8+ -Li(2s) system in order to show the influence of the Ar 8+ core electrons on the final n -distributions. The experimental and theoretical results are found to be in fair agreement except for the 9s and 9p cross sections. The presence of the projectile core electrons strongly affects the population and the collision energy dependence of low-values produced in the electron capture reaction. In particular, the σ (n ) partial cross sections (n = 8, 9 and = 0, 1, 2) increase with decreasing energies and go through a maximum for σ (8s) and σ (8p). Electronic energy curve calculations for the (Ar 7+ + Li) + and (O 7+ + Li) + systems allow us to discuss the results in terms of dynamical couplings.

Role of the projectile core in slow ion - molecule collisions: a molecular-state close-coupled treatment

“…C 4+ ) in this reaction gives rise to several successive avoided crossings that the entrance channel encounters with the neighbouring states correlating to the n = 3 manifold of the formation ion C 3+ . As noted earlier, this can also be viewed as if the presence of a finite core in the projectile has removed the degeneracy of smaller -substates within the same n-manifold in the separatedatom limit [5]. This makes the rotational couplings nearly constant and, thus, less efficient in transferring the flux.…”

“…The magnitude of the energy defect relevant to the primary mechanism of the charge transfer for reaction (2) as compared to reaction ( 1) is relatively smaller and the localization of the near crossings shifted towards the larger R region. This may make the resulting radial couplings among various states a bit more efficient [5]. The dominance of the capture into the states correlated to 3d and 3p of N 4+ , especially at lower energies, is a clear manifestation of the above-stated fact.…”

“…More than their total cross sections, it is their -distribution that demands very careful and thorough investigations, as it may carry signatures of the projectile structure, if any. For example, it has been found through a number of recent classical trajectory Monte Carlo (CTMC) calculations [5][6][7][8][9], basically a high-energy approximation, that a near statistical -distribution of the total capture cross section is retained if the incident projectile is a bare nucleus. This is a manifestation of the Stark mixing where the primary mechanism of the charge transfer is basically due to a localized radial coupling [5].…”

“…For example, it has been found through a number of recent classical trajectory Monte Carlo (CTMC) calculations [5][6][7][8][9], basically a high-energy approximation, that a near statistical -distribution of the total capture cross section is retained if the incident projectile is a bare nucleus. This is a manifestation of the Stark mixing where the primary mechanism of the charge transfer is basically due to a localized radial coupling [5]. Subsequently the Stark effect of the residual target ion over the outgoing product ion usually produces n -mixing.…”

“…In other words, the above noted radial coupling provides the primary step for the electron capture process, and then a flux mixing takes place between the degenerate n -levels. This is an obvious manifestation of Stark mixing, which is generally the most dominant mechanism leading to a nearly statistical -distribution of the partial capture cross sections in the case of a fully stripped incident ion (see [5] and references therein).…”