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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 85, NO. A5, PAGES 2171–2176, 1980

Comparison of the N₂ ⁺ Photochemistry at Different Phases of the Solar Cycle

Marsha R. Torr

Space Physics Research Laboratory, The University of Michigan, Ann Arbor, Michigan 48109

D. G. Torr

Space Physics Research Laboratory, The University of Michigan, Ann Arbor, Michigan 48109

R. A. Ong

Space Physics Research Laboratory, The University of Michigan, Ann Arbor, Michigan 48109

Abstract

Over the increasing phase of solar activity from 1974 to 1978 the F _10.7 index increased from ∼70 to ∼180. Earlier studies of the N₂ ⁺ ion based on the Atmosphere Explorer satellite measurements used data gathered in 1974. A study of N₂ ⁺ using 1978 measurements made during significantly higher solar EUV fluxes reveals a change in the relative importance of the major chemical processes. Photoionization of N₂ is found to be the major source of N₂ ⁺ in the F ₂ layer, by contrast with the charge exchange reaction of O⁺(² D) with N₂, which was dominant for the lower solar activity. The increased electron concentrations enhance the importance of reactions involving electrons, thus permitting good determinations of the relevant reaction rate coefficients, which could not be done in the earlier studies. As such, the 1978 data provide a useful opportunity to confirm the photochemical scheme established earlier and to improve the accuracy of the determination of the rate coefficients for certain processes. Specifically, we determine the rate coefficient for dissociative recombination of N₂ ⁺ with electrons, confirming laboratory measurements; we refine an earlier determination of the charge exchange rate coefficient for O⁺(² D) with N₂ to (7 ± 3) × 10⁻¹¹ cm³ s⁻¹; and we determine the rate coefficient for quenching of O⁺(² D) by electrons, confirming a theoretical calculation.

Received 14 September 1979; accepted 2 January 1980.

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Citation: Torr, M. R., D. G. Torr, and R. A. Ong (1980), Comparison of the N₂ ⁺ Photochemistry at Different Phases of the Solar Cycle, J. Geophys. Res., 85(A5), 2171–2176.

Copyright 1980 by the American Geophysical Union.