Excitation of the OI (3s 5S–3p 5P; λ7774 Å) multiplet by electron impact on O2

Abstract

We have measured the absolute cross section value and emission linewidths of the OI (3s⁵S⁰–3p⁵P; λ7774 Å) multiplet excited by electron impact on O₂. The 3p⁵P cross section, which was measured from threshold to 400 eV, is large, with a value of 4.23×10⁻¹⁸ cm² ±14% measured at 100 eV, hence this cascade feature constitutes a significant source of excitation for the OI (⁵S⁰) state. The multiplet’s emission line widths are highly Doppler broadened in dissociative excitation, and display two distinct kinetic energy distributions. These distributions indicate that both purely repulsive and discrete, bound, excited molecular states which then predissociate are involved in the dissociation process leading to the excitation of OI λ7774 Å. The magnitude of the measured cross section, and the fragment kinetic energy distribution inferred from the observed Doppler broadening both indicate that previous time‐of‐flight studies of the metastable OI (⁵S⁰) state require some reinterpretation.