  We explore model electron dynamics of an atom scattering off a surface within
the time-dependent complete active space self consistent field (TD-CASSCF)
approximation. We focus especially on the scattering of a hydrogen atom and its
resulting spin-dynamics starting from an initially spin-polarized state. Our
results reveal competing electronic time-scales that are governed by the
electronic structure of the surface as well as the character of the atom. The
timescales and nonadiabaticity of the dynamics are reported on by the final
spin-polarization of the scattered atom, which may be probed in future
experiments.
