Electron energy-loss studies of molecular oxygen in the region 6.0-16.1 eV using a multidetector electron spectrometer

The electron energy-loss spectrum of molecular oxygen, in the region 6-16 eV, has been studied under a variety of experimental conditions. Scattered electrons are detected with high efficiency by the use of a positron-sensitive multidetector. Spectra displaying an energy resolution as high as 25 meV (FWHM) are presented and discussed. A number of new transitions, forbidden by electric-dipole selection rules are seen, some of which form vibrational series. The most notable of these is a spin-forbidden series, containing three members which are superimposed on the Schumann-Runge continuum, leading to a new assignment of the d 1 Pi g state. The present spectra also provide supporting evidence for many previously reported transitions.