Transitions and the effects of configuration interaction in the spectra of Sn XV-Sn XVIII

Charge state specific euv spectra from a range of tin ions have been recorded at Tokyo Metropolitan University. The spectra were produced from charge-exchange collisions between tin ions and helium atoms using an electron cyclotron resonance source. At low target gas pressures, the spectra were dominated by single capture events. The spectra were, unexpectedly, found to be dominated by an intense unresolved transition array near 13 nm while the resonance lines, including the previously identified 4p-4d S1 0 → P1 1 resonance line of Sn XV, were relatively weak. From atomic structure calculations, it was found that the unresolved transition array arises from 4 s2 4 pm-1 4d-4 s2 4 pm-1 4f+4 s2 4 pm-2 4 d2 transitions. In addition it proved necessary to include interaction with core excited 4s4 pm 4d configurations to fully explain the observed spectra.