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| Titel |
Electron-Nitrogen Collision Processes Relevant to Planetary Atmospheres |
| VerfasserIn |
Paul Johnson, Charles Malone, Murtadha Khakoo, Jason Young, Bahar Ajdari, Xianming Liu, Joseph Ajello, Isik Kanik |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250047417
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| Zusammenfassung |
| Electron-N2 collisions play an important role in the nitrogen-rich upper atmospheres of
Titan, Triton, and Earth. Modeling these processes requires accurate laboratory
data. Despite the recognized importance of such data, there remained a poor degree
of consensus among much of the available laboratory collision cross section data
well into the present millennium. To address this situation, our group has devoted
considerable effort over the past decade to improve the status of low energy electron
collision data. In doing so, we have measured direct excitation cross sections for 17
electronic states of neutral N2 and a variety of key UV emission cross sections. Here we
review the results of this effort, highlighting how our picture of electron collision
processes has evolved, where consensus has been reached, and where discrepancies
still exist. Particular attention will be given to the excitation of the a1Î g state and
the resulting emissions, which comprise the Lyman-Birge-Hopfield (LBH) band
system.
LBH emissions are an important signature of excited N2 in the upper atmosphere of Earth
and have been clearly identified in Cassini’s Ultraviolet Imaging Spectrograph (UVIS)
measurements of Titan’s airglow. Hence, the LBH band of emissions, produced primarily
from electron impact-induced excitation of the metastable a1Î g(v′) state followed by decay
into the ground X1Σg+(v″) state, is an essential input for models of dayglow and auroral
processes in nitrogen-rich atmospheres. Here we will highlight recent efforts to
enhance our understanding of this important emission process. Specifically, we
will present recent measurements showing the total LBH cross section, a(v′,v″),
calculated in [Ajello and Shemansky, J. Geophys. Res., 90, 9845, 1985], which
was based primarily on a single LBH line, a(3,0), is incorrect. We will present
excitation cross sections for both the a(3,0) and a(2,0) vibronic transitions and
provide a revised total cross section. These new measurements [Young et al., J. Phys.
B., 43, 135201, 2010] are found to be consistent with recent electron energy-loss
measurements [Johnson et al., J. Geophys. Res., 110, A11311, 2005]. In addition, new
electron energy-loss measurements are presented for excitation of the a1Î g state, with
finely-spaced ( |
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