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Low energy differential and integral electron-impact cross sections for the 2s22p4 3P → 2p33s 3So excitation in atomic oxygen

Differential and integral cross sections (ICSs) for excitation in atomic oxygen have been measured at electron-impact energies of 15, 17.5, 20, 22.5 and 27.5 eV. Differential measurements were conducted with a conventional electron energy-loss spectrometer and a microwave discharge source of atomic oxygen. Relative differential cross sections (DCSs) were determined between 15 and 30 eV impact energy. With the help of theoretical predictions of the shape of the DCS at large angles, measured results were extrapolated to 180° scattering angle and relative ICSs were deduced. The relative excitation function was normalized to the 30 eV impact energy ICS given by Kanik et al (2001 J. Phys. B: At. Mol. Opt. Phys. 34 2647). Normalization of the ICS values allowed the measured DCSs to be put on the absolute scale. Theoretical calculations of the DCSs were carried out using the R-matrix with the pseudostates approach. A total of 22 spectroscopic bound and autoionizing states, together with 19 pseudostates, were included in the close-coupling expansion. The pseudostates were chosen to simulate continuum target states. Theoretical results, along with other available experimental data, have been compared with the current experimental results.