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. Three vibrational progressions are identified. One of them corresponds to 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 in TPE spectroscopy. Possible assignments for these progressions are discussed. The vibrational progression in the X 2PI(g), state has been seen 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 vibrational levels with v+ > 20 of the X state are seen to overlap with the a state levels. The relative contribution of both states is obtained through a deconvolution procedure. The vibrational progression in the 4SIGMA(g)- is extended to v+ = 18. The threshold photoelectron spectrum around 20 eV shows a particularly high density of lines. Possible assignments of these lines to new progressions are discussed with the help of a series of time-of-flight photoelectron spectra (TOF-PES) measured at a series of excitation energies between 18 and 20 eV.