Electron-impact studies of atomic oxygen: I. Differential and integral cross sections; experiment and theory

We report both experimental and theoretical differential and integral excit ation cross sections of atomic oxygen corresponding to the 2s(2)2p(4) P-3 - -> 3s S-3 (130.4 nm), 2s(2)2p(4) 3P --> 3d D-3 (102.7 nm), 2s(2)2p(4) P-3 - -> 3s ' D-3 (98.9 nm) and 2s(2)2p(4) P-3 --> 3s " P-3 (87.8 nm) transitions at 30, 50, and 100 eV electron-impact energies. Experimental measurements have been made in the angular range from 0 degrees to 25 degrees with a con ventional electrostatic electron energy-loss spectrometer. The atomic O dif ferential cross sections (DCSs) were put on an absolute scale by normalizat ion to the O-2 DCS values of Johnson and Kanik (2001). Extrapolation of the measured results to larger angles was performed using theoretical calculat ions as a guide, and integral cross sections were derived. Theoretical calc ulations based on the R-matrix method, along with other available experimen tal data, have been compared with the current experimental results.