  Complete sticking at low incidence energies and broad angular scattering
distributions at higher energies are often observed in molecular beam
experiments on gas-surface systems which feature a deep chemisorption well and
lack early reaction barriers. Although CO binds strongly on Ru(0001),
scattering is characterized by rather narrow angular distributions and sticking
is incomplete even at low incidence energies. We perform molecular dynamics
simulations, accounting for phononic (and electronic) energy loss channels, on
a potential energy surface based on first principles electronic structure
calculations that reproduce the molecular beam experiments. We demonstrate that
the mentioned unusual behavior is a consequence of a very strong rotational
anisotropy in the molecule-surface interaction potential. Beyond the
interpretation of scattering phenomena, we also discuss implications of our
results for the recently proposed role of a precursor state for the desorption
and scattering of CO from ruthenium.
