The Composition Of The Upper Atmosphere According to The Dissociation Of Oxygen And Nitrogen Molecules

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  • 1 Observatoire de Lyon, France
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We show that the observation of forbidden lines in the spectra of the night sky and of aurorae requires that the upper atmosphere should be composed essentially of atomic oxygen and nitrogen. The transition between molecular and atomic regions is realized abruptly for both gases towards the height of 100 km. The absorption of the ultraviolet solar radiation undoubtedly decomposes the oxygen molecules of the upper atmosphere, but the dissociation of nitrogen molecules is harder to understand. Molecular recombinations by triple collisions being unusual in the upper altitudes, we can understand that a weak dissociative source is able to maintain the atomic state of upper atmospheric layers: the most probable one is photochemical dissociation, but the effect is important only when the temperature rises above 1000° K.

We show that the observation of forbidden lines in the spectra of the night sky and of aurorae requires that the upper atmosphere should be composed essentially of atomic oxygen and nitrogen. The transition between molecular and atomic regions is realized abruptly for both gases towards the height of 100 km. The absorption of the ultraviolet solar radiation undoubtedly decomposes the oxygen molecules of the upper atmosphere, but the dissociation of nitrogen molecules is harder to understand. Molecular recombinations by triple collisions being unusual in the upper altitudes, we can understand that a weak dissociative source is able to maintain the atomic state of upper atmospheric layers: the most probable one is photochemical dissociation, but the effect is important only when the temperature rises above 1000° K.

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