Projectile Auger spectra of gas- and foil-excited oxygen ions at MeV energies

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Abstract
High-resolution projectile Auger spectra of singly and doubly core-excited oxygen ions are studied as a function of incident beam energy (2-18 MeV), exciter gas (helium, neon, argon, and krypton) or foil (carbon), incident charge state (1+ to 4+), and delay time. Auger-electron production from excited oxygen states varies considerably for collisions with different beam energies and exciter gases. A striking similarity in both the linewidths and relative Auger line intensities is observed for single-collision gas and multiplecollision foil excitation. The incident ion charge state does not appreciably affect the excitation cross sections and the charge state of the outgoing projectile. In order to assign the measured Auger peaks numerous excitation and Auger transition energies for singly and doubly core-excited states are calculated using semiempirical and ab initio methods. Calculated transition energies are compared with experimental line structures. Possible excitation and deexcitation mechanisms are suggested and discussed within a quasimolecular single-particle model.