Low-energy electron capture by N4+ ions from H atoms: Experimental study using merged beams and theoretical analysis by molecular representation.

Abstract

Measurements and theoretical analyses of total electron-capture cross sections for collisions of ${\mathrm{N}}^{4+}$ with ground-state hydrogen (deuterium) are reported in the energy range 1\char21{}300 eV/u. The present measurements have reduced relative uncertainty compared to previous absolute measurements at Oak Ridge National Laboratory [Huq et al., Phys. Rev. A 40, 1811 (1989)] and are used for detailed comparison with more recent coupled-channel molecular-orbital calculations [Shimakura et al., Phys. Rev. A 45, 267 (1992); Zygelman et al., ibid. 46, 3846 (1992)]. The most striking difference between the calculations was the increasing trend in the cross section for collision energies below 4 eV/u, as estimated by Zygelman et al. using only singlet states of the quasimolecule and the decreasing trend predicted by Shimakura et al. using both singlet and triplet states. The latter decreasing trend is consistent with the previous measurement. At 0.5 eV/u, the predicted singlet cross sections differ nearly by a factor of 2. Possible origins for this difference are explored. Strong structure is predicted in the cross section of Zygelman et al. and, to a lesser extent, in that of Shimakura et al. ; however, the phase of the structure is different in the two theories. Structures observed in the measurement at the higher collision energies are not in complete harmony with either prediction.