Vertical triple ionization of ethyne molecules in triple-electron-transfercollisions with O2+ beam ions

Triple-electron-transfer (TET) collisions of 6 keV O2+ beam ions with gas-p hase ethyne molecules were studied with mass spectrometric techniques. Meas urement of the kinetic energies of the O- ions produced yielded triple-ioni zation energies (TIEs) of ethyne to states of its triply charged positive i on, once those transitions corresponding to the transfer of three electrons in a single collision were identified: eight such peaks were found between 65.1 and 80.1 eV. Possible O2+ states in the beam include P-3, D-1, S-1; a ccording to spin conservation the singlet ions should populate only doublet states of C2H23+, while projectiles in triplet states would populate both its doublet and quadruplet states. Using ab initio propagator calculations for the triple-ionization transitions, the TIEs and quantum numbers for the states of C2H23+ associated with each peak observed in the TET spectrum co uld be identified. The overall match between the theoretical and experiment al energies was good, so that it could be established that the population o f quadruplet states was comparable in intensity with that for doublets. Thi s is consistent with previous evidence for O2+(P-3) being the dominant stat e in the projectile beam used. (C) 2000 Elsevier Science B.V. All rights re served.