Alignment of heavy few-electron ions following excitation by relativistic Coulomb collisions

Abstract

The Coulomb excitation of highly charged few-electron ions in relativistic collisions with protons and low-$Z$ atoms is studied within the framework of first-order perturbation theory and the multiconfiguration Dirac-Fock method. Apart from the computation of the total excitation cross sections, a detailed theoretical analysis has been performed for the magnetic sublevel population of the residual ions. To describe this population, general expressions are derived for the alignment parameters of the excited states of the ions, taking into account the relativistic and many-electron effects. Calculations are performed for the $K\ensuremath{\rightarrow}L$ and $K\ensuremath{\rightarrow}M$ excitation of helium- and lithiumlike uranium ions and for a wide range of projectile energies. It is shown that the alignment of heavy few-electron ions is sensitive to relativistic and magnetic-interaction effects and, hence, to the collision energies of the projectiles. The theoretical predictions are discussed in the context of recent measurements on the Coulomb excitation of heliumlike uranium ${\text{U}}^{90+}$ ions which were recently performed at the GSI storage ring in Darmstadt.