Alignment and orientation in the electron-impact excitation of H- and He-like ions.

Abstract

The alignment and orientation parameters of excited states are theoretically studied for the electron collision with H-like and He-like ions. With the use of the distorted-wave method, those parameters are calculated for the excitation of the 2 $^{1}$P and 2 $^{3}$P states of He-like ions with Z=3,8,\ensuremath{\infty} and the 2p state of H-like ions with Z=2,6,\ensuremath{\infty}. Here Z is the nuclear charge of each ion. The dependence of the parameters on the scattering angle and the collision energy is examined along the isoelectronic sequences. When compared at the same collision energy in threshold units, the parameter as a function of the scattering angle is not much changed along each isoelectronic sequence.