DIFFERENTIAL EXCITATION CROSS-SECTIONS OF MOLECULAR-OXYGEN BY ELECTRON-IMPACT - THE LONGEST AND 2ND BANDS

We have measured absolute differential excitation cross sections for t he longest and second bands of molecular oxygen by electron impact. A crossed-beam method was used. The angular range covered was 12-degrees to 156-degrees, while the impact energy range was 15 to 50 eV. Two pr onounced minima are present in the angular distributions of both cross sections, indicating in both cases substantial D-wave character. Addi tionally, the angular distributions show that both the longest and sec ond bands are composite structures, arising from a combination of elec tric dipole allowed and electric dipole forbidden transitions. We also computed integrated cross sections from the present differential cros s sections, and found a broad maximum in the former near 20-eV impact.