THRESHOLD PHOTOELECTRON-SPECTRUM OF MOLECULAR-OXYGEN IN THE REGION OFTHE B-(2)SIGMA(-)(G)[-X-(3)SIGMA(-)(G) TRANSITION

The threshold photoelectron (TPE) spectrum of isotopically substituted molecular oxygen (O-18(2)) has been measured in the region 20.2-21.6 eV in order to determine the origin of the new progression recently ob served by Baltzer et al. (Phys. Rev. A 1992, 45, 4374) by He II photoe lectron spectroscopy and by Merkt et al. (Chem. Phys. 1993, 137, 479) by threshold photoelectron spectroscopy. The adiabatic ionization pote ntial for this progression is determined to be 20.352 +/- 0.002 eV for O-16(2). Intensity perturbations in the spectrum of the B (2) Sigma(g )(-) <-- X (3) Sigma(g)(-) are also reported.