HIGH-RESOLUTION THRESHOLD PHOTOELECTRON-SPECTRUM OF MOLECULAR-OXYGEN

The threshold TPE photoelectron spectrum of molecular oxygen has been reinvestigated using a partially cooled effusive molecular jet and the monochromatised VUV synchrotron radiation from super-ACO in Orsay. Th ree vibrational progressions are identified. One of them corresponds t o and confirms that observed recently by Baltzer et al. (Phys. Rev. A 45 ( 1992) 4374), the two other ones are observed for the first time i n TPE spectroscopy. Possible assignments for these progressions are di scussed. The vibrational progression in the X 2PI(g), state has been s een up to v+ = 26 and the two spin-orbit components (2PI1/2 and 2PI3/2 ) are for the first time fully resolved in TPES. High-lying vibrationa l levels with v+ > 20 of the X state are seen to overlap with the a st ate levels. The relative contribution of both states is obtained throu gh a deconvolution procedure. The vibrational progression in the 4SIGM A(g)- is extended to v+ = 18. The threshold photoelectron spectrum aro und 20 eV shows a particularly high density of lines. Possible assignm ents of these lines to new progressions are discussed with the help of a series of time-of-flight photoelectron spectra (TOF-PES) measured a t a series of excitation energies between 18 and 20 eV.