Intermediate stages of the Rydberg-level population of multiply charged ions escaping solid surfaces

We have investigated the intermediate stages of electron capture into Rydberg states of multiply charged ions (core charge Z >> 1, principal quantum number n(A)>> 1) escaping solid surfaces at low velocity. The time-symmetrized, two-state vector model of the process is proposed by using both initial and final states of the ion-surface system. The two conditions determine two wave functions and both are used to describe the system at intermediate stages. The appropriate probabilities and rates are defined and calculated from the corresponding mixed flux. Taking into account both the surface polarization and the polarization of the electronic cloud of the ionic core, the probabilities and rates are obtained in a simple analytical form; the population of the Rydberg levels of the ions Ar VIII, Kr VIII, and Xe VIII interacting with an Al surface is considered as an example. The quasiresonant character of the process is demonstrated, as well as the complementarity of the neutralization and ionization processes for the A(Z+) ions escaping the surface and the A((Z-1)+) ions approaching the surface, respectively. The neutralization distances for the ions finally detected in a given Rydberg state are obtained from the calculated rates. Although defined under different physical conditions, the results obtained are in agreement with the coupled-angular-mode theoretical predictions.