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Dissociative recombination in planetary ionospheresIonization in planetary atmospheres can be produced by solar photoionization, photoelectron impact ionization, and, in auroral regions, by impact of precipitating particles. This ionization is lost mainly in dissociative recombination (DR) of molecular ions. Although atomic ions cannot undergo DR, they can be transformed locally through ion-molecule reactions into molecular ions, or they may be transported vertically or horizontally to regions of the atmosphere where such transformations are possible. Because DR reactions tend to be very exothermic, they can be an important source of kinetically or internally excited fragments. In interplanetary thermospheres, the neutral densities decrease exponentially with altitude. Below the homopause (or turbopause), the atmosphere is assumed to be throughly mixed by convection and/or turbulence. Above the homopause, diffusion is the major transport mechanism, and each species is distributed according to its mass, with the logarithmic derivative of the density with repect to altitude given approximately by -1/H, where H = kT/mg is the scale height. In this expression, T is the neutral temperature, g is the local acceleratiion of gravity, and m is the mass of the species. Thus lighter species become relatively more abundant, and heavier species less abundant, as the altitude increases. This variation of the neutral composition can lead to changes in the ion composition; furthermore, as the neutral densities decrease, dissociative recombination becomes more important relative to ion-neutral reactions as a loss mechanism for molecular ions.
Document ID
19950063648
Acquisition Source
Legacy CDMS
Document Type
Conference Paper
Authors
Fox, J. L.
(State University of New York, Stony Brook, NY, US, United States)
Date Acquired
August 17, 2013
Publication Date
January 1, 1993
Publication Information
Publisher: Plenum Press (NATO Advanced Science Institute (ASI) Series B: Physics, Vol. 313)
Subject Category
Geophysics
Accession Number
95A95247
Funding Number(s)
CONTRACT_GRANT: NAGW-523
CONTRACT_GRANT: NAGW-2483
CONTRACT_GRANT: NADW-2238
Distribution Limits
Public
Copyright
Other

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