Measurement of absolute differential excitation cross sections of molecular oxygen by electron impact: Decomposition of the Herzberg pseudocontinuum

Using a crossed-beam method, we have measured electron energy-loss spectra for excitation of the Herzberg pseudocontinuum of molecular oxygen. The scattering angle and electron-impact energy ranges covered were from 12° to 156° and from 10 to 30 eV, respectively. We decomposed the spectra into contributions from three superposed Gaussian line shapes by means of computerized least-squares analysis. The three line shapes were identified as representing excitation of the A³Σ_u⁺, A^′3Δ_u, and c¹Σ_u^- states. Absolute differential and integrated cross sections for all three states’ excitations were obtained, along with linear electronic potential-energy curves for the Franck-Condon region.