Shell- and subshell-resolved projectile excitation of hydrogenlike Au78+ions in relativistic ion-atom collisions

Abstract

The projectile excitation of high-$Z$ ions has been investigated in relativistic ion-atoms collisions by observing the subsequent x-ray emission. The x-ray spectra from the projectile excitation have been separated from the x-ray emission following electron capture into the excited states using a novel anticoincidence technique. For the particular case of hydrogenlike Au${}^{78+}$ ions colliding with Ar atoms, Coulomb excitation from the ground state into the fine-structure-resolved $n=2$ levels as well as into levels with principal quantum number $n\ensuremath{\geqslant}3$ has been measured with excellent statistics. The observed spectra agree well with simulated spectra that are based on Dirac's relativistic equation and the proper inclusion of the magnetic interaction into the amplitudes for projectile excitation. It is shown that a coherent inclusion of the magnetic part of the Lienard-Wiechert potential leads to the lowering of the excitation cross section by up to 35%. This effect is more pronounced for excitation into states with high angular momentum and is confirmed by our experimental data.