Direct experimental measurement of electron impact ionization‐excitation branching ratios 4. Branching ratios and cross sections for O 2 + at 100 eV

• Published in: Journal of Geophysical Research: Space Physics 1997-05, Vol.102 (A5), p.9691-9696
• Main Authors: Doering, J. P., Yang, J.
• Format: Article
• Language: English
• ISSN: 0148-0227
• DOI: 10.1029/96JA03997

The 100‐eV ionization of molecular oxygen has been studied by the ( e ,2 e ) electron‐electron coincidence method. Ionization to the ground state and five excited states of O 2 + has been detected. Of these six electronic states, ionization to three, the X 2 Π g , a 4 Π u , and b 4 Σ g − states, was found to account for approximately 95% of the O 2 + production. Relative triple differential cross sections for the production of O 2 + in these three states were measured as a function of ejected electron energy, ejected electron angle, and incident electron scattering angle. Ionization to the three higher energy states, B 2 Σ g − , 2 Π u , and c 4 Σ u − , was found to be much weaker, and it was only possible to estimate the branching ratios to these states. Ionization to the A 2 Π u state, the upper state of the second negative bands of O 2 + , was not observed, as this state is only weakly excited and is overlaid by the stronger a 4 Π u state. The branching ratios were found to be 0.540, 0.297, and 0.122 for the X 2 Π g , a 4 Π g , and b 4 Σ g − states, respectively. The total branching ratio for the B 2 Σ g − , 2 Π u , and c 4 Σ u − states was 0.042 (all values ±20%). The branching ratio to the A 2 Π u state was estimated to be