Mg+(3p) excitation amplitudes in slow Mg+-Ar collisions

Abstract
The probabilities and amplitudes for exciting the magnetic sublevels of Mg+(3p) in collisions between accelerated Mg+ ions and Ar atoms have been studied by means of the polarised-photon, scattered-ion coincidence technique. Selected collision energies and scattering angles within the ranges 1.2-11 keV and 0.9-9 degrees were chosen. The excitation probability for the Mg+(3p) configuration shows an apparent angular threshold. A special effort was made to determine the amplitudes in the region of this threshold. Strongly polarised charge distributions are formed in the individual collisions. The direction of this polarisation is parallel to the collision plane and in most cases nearly perpendicular to the beam direction. In the region of the apparent angular excitation threshold it starts turning within the collision plane. In close collisions at high energies some degree of circular polarisation is observed.