THERMALIZATION OF FAST NITROGEN-ATOMS IN ELASTIC AND INELASTIC-COLLISIONS WITH MOLECULES OF ATMOSPHERIC GASES

The energy relaxation of fast nitrogen atoms due to elastic and inelas tic collisions with molecules in the atmosphere is studied. A new form ula for the energy relaxation kernel in the Boltzmann kinetic equation , which applies equally to elastic and inelastic collisions, is derive d. Angular and energy dependent differential cross sections are used i n calculations of the energy transfer rate. The energy relaxation kern el is evaluated for inelastic N+N-2 collisions with numerically determ ined differential cross sections for rotational and vibrational excita tion of the N-2 molecules. The mean rate of energy loss, the average e nergy transfer per collision and mean thermalization times are calcula ted as functions of the kinetic energy of the nitrogen atoms. The cont ributions of elastic and inelastic scattering to the thermalization of N atoms in the terrestrial atmosphere are analyzed. The energy distri bution functions of the fast nitrogen atoms are evaluated for thermosp heric conditions. They depart significantly from a Maxwellian distribu tion at high energies. (C) 1998 Elsevier Science Ltd. Al rights reserv ed.