DYNAMIC THRESHOLDS FOR THE EXISTENCE OF EXCITED ELECTRONIC STATES OF FAST IONS IN SOLIDS

We calculate eigenenergies for bound states of electrons in the dynamical screening potential of a fast charged particle traversing a solid by diagonalization of Hamiltonian matrices in a truncated Hilbert space of 600 hydrogenic basis states. Application of classical scaling invariances yields a universal energy-level diagram. A simple approximate formula for projectile-centered one-electron bound states is obtained. We find velocity thresholds for the existence of excited states which are in surprisingly good agreement with recent data by Chevallier et al. [Phys. Rev. A 41, 1738 (1990)].