Why nitric oxide lights up the sky
A new study shows that electron interactions may have nearly the same importance as chemical luminescence in exciting the atmospheric molecules that cause auroras. Campbell et al. suggest that nitric oxide molecules are promoted into potentially glowing, vibrational excited levels by a short-lived negative ion that is formed as a result of electron impact. Previous studies had reported that chemiluminescence, where nitrogen and oxygen molecules interact to form excited nitric oxide, was the main source of auroral lights produced by nitric oxide molecules. The authors analyzed the electron interactions with nitric oxide molecules in the upper atmosphere and found that the momentary (10-100 femtoseconds or quadrillionths of a second) creation of a negative ion increases the probability of producing the excitation levels that are responsible for auroral lights by up to two orders of magnitude.
They suggest that the electron-driven effect results from a chance convergence of nitric oxide’s molecular structure and the natural distribution of electrons in the upper atmosphere.
Title: Infrared auroral emissions driven by resonant electron impact excitation of NO molecules
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