Identification of very low energy projectile Coster-Kronig transitions in high velocity collisions using zero-degree Auger electron spectroscopy

The unusual looking open-quotes mesaclose quotes-shaped cusp observed in O3+ collisions with He has been investigated using zero-degree electron spectroscopy, in both high resolution for collision energies of 10, 15 and 23 MeV and in lower resolution, but in coincidence with the outgoing charge-analysed projectile, at 10 MeV. The high resolution studies indicate the open-quotes mesaclose quotes peak to be actually composed of primarily two very strong antoionizing peaks (other than the cusp peak) corresponding to energies of 0.053 ± 0.005 and 0.103 ± 0.010 eV in the emitter frame. The coincidence studies, indicate these lines to originate from excitation of the O3+ ion followed by autoionization. Ongoing Hartree-Fock-Slater calculations, severely tested at these extremely small transition energies, indicate that these lines could result from the Coster-Kronig deexcitation of O3+(1s22s2pnl) Rydberg states produced during the collision. Furthermore, the unusually sharp edges of these lines giving rise to the characteristic open-quotes mesaclose quotes-shape look, can be shown to be consistent with the kinematic constraints imposed by the energy and angular acceptance range of the spectrometer