  We consider a Hamiltonian system that models the scattering of helium atoms
off a copper surface. The interaction between the He and the Cu atoms is
described by a corrugated Morse potential. Using corrugation coefficients
values in the potential obtained by fitting to experimental values, we prove
that, provided some coefficient of an auxiliary function is different from 0,
there are regions of the phase space, corresponding to sufficiently large
energy of the incident atom, where the scattering is chaotic. Furthermore, we
prove that the system has oscillatory motions.
