On the direct and dissociative excitation of the O(3s3S0) state by electron impact on atomic and molecular oxygen

Publisher Website
Google Scholar
Abstract
The excitation of the O (3s 3S0 to 2p 3P; lambda 1304 AA) resonance transition by electron impact on atomic and molecular oxygen has been studied. The ratio of the cross sections for the specific atomic and dissociative processes, sigma A/ sigma D, has been measured accurately from 60 to 300 eV by direct normalisation to the ratio of the specific O+ and O2+ ionisation cross sections. At 100 eV, sigma A/ sigma D=3.00+or-9%. The experiment was carried out using an apparatus that combined a high-density diffuse gas source (n(O) approximately 1012 cm-3), an electrostatically focused electron gun, a vacuum-ultraviolet monochromator and a quadrupole mass spectrometer for simultaneous optical and composition measurements. The present sigma A/ sigma D values are smaller by a factor of 2.1 than the original results of Stone and Zipf (1974) and Mumma and Zipf (1971). When revised sigma A(1304 AA) values are calculated from these new data using contemporary calibration standards, it is found that the shape of the cross section for the excitation of the O (3s 3S0) state by electron impact on atomic oxygen agrees well with the earlier work but the absolute magnitude of sigma A(1304 AA) must be reduced by a factor of 2.8. The revised cross section values are in good agreement with recent quantum calculations when cascade excitation of the 3s 3S0 state is taken into account.