Rotationally resolved pulsed field ionization photoelectron bands for O2+(a 4Πu, v+=0–18) in the energy range of 16.0–18.0 eV

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 4Πu, v+=0–18,J+)←O2(X 3Σg., v″=0,N″). Although these vibrational PFI-PE bands for O2+(a 4Πu, v+) have significant overlaps with those for O2+(X 2Πg) and O2+(A 2Πu), we have identified all O2+(a 4Πu, v+=0–18) bands by simulation of spectra obtained using supersonically cooled O2 samples with rotational temperatures ≈20 and 220 K. While the v+=4–18PFI-PE bands represent the first rotationally resolved photoelectron data for O2+(a 4Πu), the PFI-PE bands for O2+(a 4Πu, v+=10–18) 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 2Πu, v+=0–18). The observed intensities of spin–orbit components for the majority of O2+(a 2Πu, v+) vibrational bands are in accordance with the forced spin...