Fast Ion-Atom Collisions: Electron Spectroscopy of Mixed-State Beams

The problem of the dynamics of many-body quantum systems under intense and ultra-fast perturbations is ideally addressed in energetic collisions of few-electron ions with atomic targets. Collisions with multiunpaired electron-ion cores, offered by mixed-state ion beams, are most challenging for studying electron dynamics, both theoretically and experimentally. Here, we present the recent advances of our experimental and theoretical work in the field of fast ion-atom collisions with mixed-state ion beams. The fundamental processes of single electron capture (SEC) and transfer excitation (TE) are revisited under new experimental results and a theoretical treatment within a three-active electron close-coupling approach (3eAOCC). In SEC, our results invalidated the frozen core approximation and related spin statistics populations, additionally proposing a distinctive screening effect due to the Pauli exclusion principle (Pauli shielding). In TE, 3eAOCC theory fills the gap of a long awaited coherent treatment of the TE process that includes its resonant and nonresonant features, showing excellent agreement with the measurements, and proposing a new nonresonant one-step TE mechanism. The report also includes the description of the basic principles of the experimental methods and the used instrumentation, as well as techniques for the experimental treatment of the mixed-state beams.