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MARTIN SCHÄFER, MATTHIAS RAUNHARDT, NICOLAS VANHAECKE AND FRÉDÉRIC MERKT, ETH Zürich, Laboratorium für Physikalische Chemie, Wolfgang-Pauli-Strasse 10, 8093 Zürich, Switzerland.
A supersonic beam of metastable He* atoms and He2* a 3
u+ molecules has been generated using a pulsed discharge at the exit of a pulsed valve prior to the gas expansion into vacuum. Pulsed-field-ionization zero-kinetic-energy (PFI-ZEKE) photoelectron spectra of the He2+ X+ 2
u+ (v+\!=\!0-2)
He2* a 3
u+ (v''\!=\!0-2) transitions and photoionization spectra of He2* in the vicinity of the lowest ionization thresholds have been recorded. The energy level structures of 4He2+ X+ 2
u+ (v+\!\leq\!2, N+\!\leq\!23) and 3He2+ X+ 2
u+ (v+\!=\!0, N+\!\leq\!11) have been determined, and an accurate set of molecular constants for all isotopomers of He2+ has been derived in a global analysis of all spectroscopic data reported to date on the low vibrational levels of He2+. \footnote D. S. Ginter, M. L. Ginter, J. Mol. Spectrosc. \textbf82, 152--175 (1980). N. Yu and W. H. Wing, Phys. Rev. Lett. \textbf59, 2055--2058 (1987), Phys. Rev. Lett. \textbf60, 2445 (1988). The analysis of the photoionization spectrum by multichannel quantum defect theory has provided a set of parameters describing the threshold photoionization dynamics of He2* a 3
u+.