Electron energy-loss studies of molecular oxygen in the region 14.8-20.3 eV using a multidetector electron spectrometer

A new, differentially pumped, multidetector electron spectrometer has been constructed and has been used to study the energy-loss spectrum of molecular oxygen. Spectra are presented with an energy resolution of approximately 30 meV (FWHM), in the energy-loss range 14.8-20.3 eV. Observation of the relative intensities of spectral features as a function of scattering conditions leads to the assignment of four new Rydberg series. Transitions from the ground state of the molecule to states in these series are symmetry forbidden. Two of the series converge on the fourth ionisation potential at 18.17 eV and two on the level at 20.296 eV, each pair comprising an ns sigma g and an nd sigma g series. Several other isolated, spin-forbidden transitions are also observed.