Vertical triple ionization of ethyne molecules in triple-electron-transfer collisions with O2+ beam ions Original Research Article

Triple-electron-transfer (TET) collisions of 6 keV O2+ beam ions with gas-phase ethyne molecules were studied with mass spectrometric techniques. Measurement of the kinetic energies of the O− ions produced yielded triple-ionization energies (TIEs) of ethyne to states of its triply charged positive ion, 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 3P, 1D, 1S; according 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 could be identified. The overall match between the theoretical and experimental energies was good, so that it could be established that the population of quadruplet states was comparable in intensity with that for doublets. This is consistent with previous evidence for O2+(3P) being the dominant state in the projectile beam used.