Pulsed-field-ionization zero-kinetic-energy photoelectron spectroscopy of metastable He2:: Ionization potential and rovibrational structure of He2+

A supersonic beam of metastable He* atoms and He(2)* a (3)Sigma(+)(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 photoelectron spectra of the He(2)(+) X(+) (2)Sigma(+)(u) (nu(+)=0-2)<- He(2)* a (3)Sigma(+)(u) (nu ''=0-2) transitions and photoionization spectra of He(2)(*) in the vicinity of the lowest ionization thresholds have been recorded. The energy level structures of (4)He(2)(+) X(+) (2)Sigma(+)(u) (nu(+)<= 2,N(+)<= 23) and (3)He(2)(+) X(+) (2)Sigma(+)(u) (nu(+)=0,N(+)<= 11) have been determined, and an accurate set of molecular constants for all isotopomers of He(2)(+) has been derived in a global analysis of all spectroscopic data reported to date on the low vibrational levels of He(2)(+). The analysis of the photoionization spectrum by multichannel quantum defect theory has provided a set of parameters describing the threshold photoionization dynamics. (c) 2008 American Institute of Physics.