NONTHERMAL NITROGEN-ATOMS IN THE EARTHS THERMOSPHERE .1. KINETICS OF HOT N(S-4)

A nonequilibrium kinetic model is used to calculate the energy distribution of translationally hot nitrogen atoms in the thermosphere. It is found that dissociation by solar EUV photons and photoelectrons provide an important source of non-maxwellian high energy N(4S) atoms. We show that quenching of metastable N(2D) atoms by atomic oxygen also produces significant amounts of hot N(4S) atoms. A numerical simulation of the hot N(4S) atom kinetics show that these atoms are present in sufficient quantity in the thermosphere to play a role in the odd nitrogen chemistry and energetics of this atmospheric region. The steady state population of hot nitrogen is obtained by taking into account the relaxation by elastic collisions and high energy reaction with O2 to form nitric oxide. It is found that the fraction of hot N atoms reacting with O2 is about 15 % 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.