Rotationally resolved pulsed field ionization photoelectron bands

We have obtained rotationally resolved pulsed field ionization-photoelectron ~PFI-PE! spectra of O2 in the energy range of 16.0–18.0 eV, covering ionization transitions O2 (a Pu , v 50 – 18,J) ←O2(X Sg , v950,N9). Although these vibrational PFI-PE bands for O21(a Pu , v) have significant overlaps with those for O2 (X Pg) and O2 (A Pu), we have identified all O2 (a Pu , v 50 – 18) bands by simulation of spectra obtained using supersonically cooled O2 samples with rotational temperatures '20 and 220 K. While the v54 – 18PFI-PE bands represent the first rotationally resolved photoelectron data for O2 (a Pu), the PFI-PE bands for O2 (a Pu , v 510– 18) are the first rotationally resolved spectroscopic data for these levels. The simulation also allows the determination of accurate ionization energies, vibrational constants, and rotational constants for O2 (a Pu , v 50 – 18). The observed intensities of spin–orbit components for the majority of O2 (a Pu , v ) vibrational bands are in accordance with the forced spin–orbit/ rotational autoionization mechanism. © 2000 American Institute of Physics. @S0021-9606~00!02003-1#