State- and isotope-dependent charge transfer of with atomic hydrogen in astrophysical and fusion plasmas

Abstract

State-and target-isotope-dependent cross sections for electron capture in collisions of N 4+ (2s) with H(1s), D(1s), and T(1s) are presented for the energy range 0.01-6000 eV amu −1 . Results are given for capture via radial coupling into the N 3+ 2s3s 1 S, 2s3p 1 P o , 2s3d 1 D, 2s3s 3 S, 2s3p 3 P o , 2s3d 3 D, and 2p3s 3 P o states and are obtained through a close-coupled, quantummechanical, molecular-orbital method. Fully ab initio molecular data determined with the spincoupled valence-bond method are incorporated. Rate coefficients for temperatures between 1000 and 10 6 K are also presented. Applications to astrophysical environments and laboratory plasmas are addressed. The importance of state-dependent parameters for the modelling of nebulae emission lines and for fusion plasma impurity diagnostics and the potential significance of isotope effects to models of the edge region of a tokamak device are briefly discussed.

Isotope effect in charge-transfer collisions of H with He+

“…In this case, we still observe wider peaks in the partial cross section for T than for H, but the magnitude of the peaks is much smaller for the heavier isotope at low energy, resulting in a decrease of the cross section. This behavior of the partial cross sections has been observed in other systems such as N 4+ + H [7] or Si 4+ + He [24]. Finally, we computed the cross section with and without the rotational couplings in order to estimate their effect, and found the effect to be negligible.…”

“…These authors interpreted this effect with the Landau-Zener-Stueckelberg model and suggested that it could occur at energies as high as 1 keV/amu for some systems. Moreover, it was established that the cross section decreases with increasing system reduced mass [7], a behavior that has since been observed in other charge-transfer collisions [8,9]. Recently, Stolterfoht et al [10,11] observed a very important isotope effect in collisions between He 2+ and H, the replacement of H by D or T leading to a variation of the cross section for energies as high as 300 eV/amu.…”

Measurement of Anomalously Strong Emission from the1s−9pTransition in the Spectrum of H-Like Phosphorus Following Charge Exchange with Molecular Hydrogen

“…Nonstatistical triplet ratios have been measured in charge exchange between N 4+ and H or H 2 [31]. Those measurements are in agreement with the fully quantal closecoupled molecular orbital calculations of Stancil et al [32]. However, in the case of our measurement it is significant that captures involving two closely neighboring ion species do not follow the same trend.…”

EBIT charge-exchange measurements and astrophysical applications

“…These spectra are somewhat more complicated than H-like spectra because the spins of the two electrons in He-like ions couple to yield either a singlet (S = 0) or triplet (S = 1) state. A 1:3 probability ratio is usually assumed based on the statistical weight of the levels, but statistical weights have been shown to be incorrect for some circumstances both experimentally and in detailed theoretical calculations [100,131] for Be-like ions, which also have S = 0 and S = 1 states. Figures 19 and 20 show schematic energy level diagrams for electron capture into n = 4 singlet and triplet states, respectively, assuming a uniform distribution of angular momentum states for illustrative purposes.…”