Abstract
A new variable angle and incident energy electron energy loss spectrometer coupled to a supersonic jet expansion microwave discharge source has been constructed to study the electron scattering cross sections of stable and unstable atmospheric species. This apparatus was specifically designed to operate at low incident electron energies and at high scattering angles to observe forbidden transitions. In this paper we report the first measurements of the absolute differential and integral cross sections of the atomic oxygen (2p4 ³P‐3p ³P), 10.99 eV, and (2p4 ³P‐3p 5P), 10.76 eV, transitions at a single electron impact energy of 30 eV. The direct excitation cross section ratio for the ³P and 5P states was found to be 6:1 which confirms previous suggestions that electron impact on O I is responsible for the observed 8446 Å and 7774 Å, O I emissions in the dayside cusp region. Additional sources of O I 3p 5P are necessary to explain the nightside auroral 8446 Å/7774 Å ratio. The absolute cascade‐free direct excitation integral cross sections for O I(³P‐³P) and O I(³P‐5P) at 30 eV are 4.0 × 10−18 cm² and 0.67 × 10−18 cm², respectively.
Published Version
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