Dipole polarization in coherently excited Stark manifolds

Abstract

The dipole polarization of a coherently excited Stark manifold is studied for the simplest case of n = 2. In addition to the well-known observables (L⊥, γ) for coherent excitation of the 2p component, we explore the opportunities provided by the degeneracy of the 2s and 2p states in a purely Coulombic system. This degeneracy allows for additional observables (D, ε) that define the size and direction of the electron charge-cloud polarization. As an example, simultaneous ionization–excitation of He+(n = 2) by electron impact is discussed. Calculations of these observables for impact energies of 5640 eV and 1585 eV are shown, together with the corresponding polarized n = 2 charge-cloud densities. For ejection angles of the slow electron within 90° of the momentum-transfer direction, these calculations predict that the excited electron is preferably located on the side of the nucleus opposite to the ejected electron. For larger ejection angles, the situation is reversed.