Theoretical Studies of Important Processes in Planetary and Comet Atmospheres
Abstract
During the past year, we have made considerable progress in our calculations of the dissociative recombination (DR) of OH(+) and O2(+) with an electron, e(-). For OH(+), DR is described by OH(+) + e(-) yields 0 + H. Calculations have been performed on a new DR mechanism which had not been calculated previously for any molecular ion. In the new mechanism, electron capture first occurs into an intermediate neutral Rydberg state that has an excited ion core. This state is predissociated by a repulsive state that generates the atomic products. This mechanism differs significantly from the well known indirect recombination mechanism where capture occurs into a state with the same core as that of the ion. The new mechanism for indirect recombination is qualitatively different from the older mechanism and involves new matrix elements. Capture can now occur into the lowest vibrational level of an intermediate Rydberg state but was restricted to only excited levels in the older mechanism. These new calculations supplement results reported previously by us for OH(+). In the new calculations, we have described capture by the v=O level of the X3Sigma- ground state of OH(+) into the a 2Pi Rydberg state consisting of the OH(+)A3 Pi core plus a Rydberg electron in a mostly 3s like orbital. Because the Rydberg state is shifted to large R relative to the ground state ion, Franck-Condon factors favor capture into the v=l intermediate level over capture into v=O. This state is predissociated by the dominant dissociative channel, 22fl . The energetics are such that the intermediate core excited state leads to pronounced structure in the DR cross section near 0.7geV. These core excited states are likely to play a role in the DR of other molecules (e.g. O(+) and N(+)) and will be the subject of future studies.
- Publication:
-
NASA STI/Recon Technical Report N
- Pub Date:
- January 1996
- Bibcode:
- 1996STIN...9622462G
- Keywords:
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- Planetary Atmospheres;
- Cometary Atmospheres;
- Electron-Ion Recombination;
- Hydroxyl Radicals;
- Atmospheric Chemistry;
- Electron Capture;
- Oxygen Ions;
- Ion Recombination;
- Atmospheric Composition;
- Molecular Ions;
- Electron Transitions;
- Lunar and Planetary Exploration