  Excited atomic nitrogen atoms play an important role in plasma formation in
hypersonic shock-waves, as happens during spacecraft reentry and other high
velocity vehicle applications. In this study, we have thoroughly studied
collision induced excitation (CIE) associated with two colliding nitrogen atoms
in the N(4S), N(2D) and N(2P) states at collisions energies up to 6 eV, using
time-independent scattering calculations to determine cross sections and
temperature-dependent rate coefficients. The calculations are based on
potential curves and couplings determined in earlier MRCI calculations with
large basis sets, and the results are in good agreement with experiment where
comparisons are possible. To properly consider the spin-orbit coupling matrix,
we have developed a scaling method for treating transitions between different
fine-structure components with calculations that only require calculations with
two coupled states, and with this we define accurate degeneracy factors for
determining cross sections and rate coefficients that include all states. The
results indicate that both spin-orbit and derivative coupling effects can play
important roles in collisional excitation and quenching, and that although
derivative coupling is always much stronger than spin-orbit, there are many
transitions where only spin-orbit can contribute. As part of this, we identify
two distinct pathways associated with N(2D) relaxation, including one
Auger-like mechanism leading to 2N(2D) that could be important at high
temperature.
