  With an eye on plasma walls we investigate, within an effective model for the
two active electrons involved in the process, secondary electron emission due
to Auger de-excitation of metastable nitrogen $N_2(^3\sigma^+_u)$ molecules at
metallic surfaces. Modelling bound and unbound molecular states by a LCAO
approach and a two-center Coulomb wave, respectively, and the metallic states
by the eigenfunctions of a step potential we employ Keldysh Green's functions
to calculate the secondary electron emission coefficient $\gamma_e$ retaining
for the Auger self-energy the non-locality in time and the dependence on the
single particle quantum numbers. For the particular case of a tungsten surface
we find good agreement with experimental data indicating that the relevant
Auger physics is well captured by our easy-to-use model.
