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| Titel |
First measurement of the dissociative recombination of CaO+ with electrons brings closure to Ca ion recycling chemistry in the lower thermosphere |
| VerfasserIn |
David Bones, John Plane |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250126935
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| Publikation (Nr.) |
 EGU/EGU2016-6731.pdf |
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| Zusammenfassung |
| Modelling the temporal and spatial extent of the metal layers in the mesosphere/lower
thermosphere requires knowledge of the rate coefficients of dissociative recombination of
metal oxide ions with electrons. Previously, these coefficients have been assumed to be 3 ×
10−7 cm3 s−1 at 200 K. In this study the coefficient has been measured directly for the
dissociative recombination of CaO+.
Measurements are made in a flowing afterglow system with a Langmuir probe. Calcium oxide
ions are introduced into an argon ion/electron plasma by pulsed laser ablation of a
solid target. The relative concentration of CaO+ is measured by a quadrupole mass
spectrometer as a function of flow rate (3 – 5 slm), which is inversely proportional to
the reaction time of the CaO+ ions with the electrons in the plasma (2.1 to 3.5
ms).
Charge transfer reactions between argon ions and neutral molecules complicate the analysis.
A kinetic model describing gas-phase chemistry and diffusion to the reactor walls
was fitted to the experimental data to extract the DR rate coefficient for CaO+.
Unlike other metals present in the atmosphere, Ca+ ions are far more abundant than
neutral Ca. The new DR rate coefficient is used to explore possible reasons for
this anomaly in a model of meteor-ablated calcium in the mesosphere and lower
thermosphere. |
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