  Using smoothed particle hydrodynamics we model giant impacts of Super-Earth
mass rocky planets between an atmosphere-less projectile and an atmosphere-rich
target. In this work we present results from head-on to grazing collisions. The
results of the simulations fall into two broad categories: 1) one main
post-collision remnant containing material from target and projectile; 2) two
main post-collision remnants resulting from `erosive hit-and-run' collisions.
All collisions removed at least some of the target atmosphere, in contrast to
the idealised hit-and-run definition in which the target mass is unchanged. We
find that the boundary between `hit-and-run' collisions and collisions that
result in the projectile and target accreting/merging to be strongly correlated
with the mutual escape velocity at the predicted point of closest approach. Our
work shows that it is very unlikely for a single giant impact to remove all of
the atmosphere. For all the atmosphere to be removed, head-on impacts require
roughly the energy of catastrophic disruption (i.e. permanent ejection of half
the total system mass) and result in significant erosion of the mantle. We show
that higher impact angle collisions, which are more common, are less efficient
at atmosphere removal than head-on collisions. Therefore, single collisions
that remove all the atmosphere without substantially disrupting the planet are
not expected during planet formation.
