SELECTIVE RYDBERG-LEVEL POPULATION OF MULTIPLY-CHARGED IONS AT SOLID-SURFACES - A DYNAMIC THEORY FOR LOW-ANGULAR-MOMENTUM IONIC STATES

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 almost-equal-to 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 st ates (l = 0, 1, and 2) is proposed. Specific features of the Rydberg s tates and ions (large size, high degeneracy with respect to 1, high va lue of Z) are included in the model. The electron transition amplitude is calculated as a mixed electron-density flux through a moving Firso v plane, whose kinematics is determined by a variational requirement. A multichannel character of the process is taken into account in the f ramework of a statistical treatment of decoupled channels, based on th e approximation of small transition probabilities. The population prob ability P(nl)=P(nl)(v,Z) of the (n,l) state is in sufficiently good ag reement with available beam-foil experimental data (S VI, Cl VII, Ar V III) not only as a function of the principal quantum number n, but als o as a function of l and v. An ''anomalous'' peak at n = 11 in the pop ulation probability of Ar VIII is briefly discussed from the standpoin t of the developed formalism. The predicted maxima in the v dependence of P(nl)(v,Z) in the intermediate velocity region calls for further m ore refined experimental studies.