Absolute experimental differential and integral electron excitation cross sections for atomic oxygen: 1. The (³P → ³So) Transition (1304 Å) at 100 eV

Abstract

The absolute differential electron scattering cross section for the atomic oxygen (³P → ³So) transition (1304 Å) has been measured at 100‐eV electron impact energy. The experimental apparatus was a variable angle and incident energy electron spectrometer coupled to a microwave discharge free supersonic jet expansion source. The source produced an intense jet containing O2, H, O, and He with an O/O2 ratio typically greater than 2.5. Relative densities of species in the jet were determined from the zero angle forward electron energy loss spectrum and the known optical oscillator strengths for transitions in each species. Measured relative differential cross sections (DCS) were put on an absolute scale by comparison with the known DCS for the He 2 ¹P transition. As a check on the atomic oxygen values a simultaneous determination was made of the DCS for the H (1s) → H (n = 2) transition. Results for this transition were in excellent agreement with previous experimental and theoretical results. An additional check on the DCS values for O and H was given by the extrapolation within experimental error of the generalized oscillator strengths calculated from the measured DCS values to the optical oscillator strengths at zero momentum change. The O ³So DCS is extremely forward peaked and decreases by almost 5 orders of magnitude from 0° to 90° scattering angle. The integral, direct excitation, cascade‐free cross section at 100 eV is 6.4 (±1.0) × 10−18 cm².