Collision Cross Sections for the Excitation of the Schumann-Runge Dissociation Continuum in Molecular Oxygen by 20-110-keV Protons

Absolute cross sections for the excitation of the Schumann-Runge dissociation continuum of molecular oxygen have been obtained from inelastic energy-loss spectra induced by 20-110-keV protons incident on gaseous targets of molecular oxygen. Apparent differential energyloss cross sections, ionization cross sections, and total inelastic cross sections are also obtained from the energy-loss spectra. The proton energy-loss spectra have an energy resolution of about 2 eV. The energy location of the first peak in the energy-loss spectra of ${\mathrm{O}}_2$ is in general agreement with the findings of photoabsorption and electron energy-loss-spectra measurements. The cross section for the Schumann-Runge dissociation continuum for 20-110-keV protons varies between 5 and 7 × ${10}^{-17\mathrm{}}$ ${\mathrm{cm}}^2$ and has a broad maximum at about 60 keV. Existing theoretical treatments show poor agreement with these reported cross sections for the excitation of the dissociation continuum with respect to both absolute magnitude and curve shape.