Selective Rydberg-level population of multiply charged ions at solid surfaces: A dynamic theory for low-angular-momentum ionic states.

Abstract

Selective Rydberg-level population of multiply charged ions (e.g., Z=6, 7, and 8) at solid surfaces is treated in normal emergence geometry. For the intermediate ionic velocity region (between v\ensuremath{\approxeq}1 and 3 a.u.) a molecular-dynamics-type model of the electron pickup process from the solid valence band into low-angular-momentum ionic states (l=0, 1, and 2) is proposed. Specific features of the Rydberg states and ions (large size, high degeneracy with respect to l, high value of Z) are included in the model. The electron transition amplitude is calculated as a mixed electron-density flux through a moving Firsov plane, whose kinematics is determined by a variational requirement. A multichannel character of the process is taken into account in the framework of a statistical treatment of decoupled channels, based on the approximation of small transition probabilities. The population probability ${\mathit{P}}_{\mathit{n}\mathit{l}}$=${\mathit{P}}_{\mathit{n}\mathit{l}}$(v,Z) of the (n,l) state is in sufficiently good agreement with available beam-foil experimental data (S VI, Cl VII, Ar VIII) not only as a function of the principal quantum number n, but also as a function of l and v. An ``anomalous'' peak at n=11 in the population probability of Ar VIII is briefly discussed from the standpoint of the developed formalism. The predicted maxima in the v dependence of ${\mathit{P}}_{\mathit{n}\mathit{l}}$(v,Z) in the intermediate velocity region calls for further more refined experimental studies.