Non thermal nitrogen atoms in the earth's thermosphere. I - Kinetics of hot N(4S). II - A source of nitric oxide

The energy distribution of translationally hot nitrogen atoms in the thermosphere has been calculated using a nonequilibrium kinetic model. Dissociation by solar EUV photons and photoelectrons is found to provide an important source of non-Maxwellian high energy N(4S) atoms. It is shown that quenching of metastable N(2D) atoms by atomic oxygen also produces significant amounts of hot N(4S) atoms. The fraction of hot N atoms reacting with O2 is found to be about 15 percent of the production rate of atomic nitrogen by N2 dissociation by photon and photoelectron impact and quenching of N(2D) metastable atoms by atomic oxygen. The very fast reaction between hot N(4S) atoms and O2 is shown to provide an additional source of nitric oxide. At equatorial latitudes, this contribution amounts to 6-30 percent of the other classical production sources of NO for solar minimum activity conditions. It is concluded that the effect of hot N atoms must be considered in future models of the NO-N system chemistry.