  Quantum reflection is a universal property of atoms and molecules when
scattered from surfaces in ultracold collisions. Recent experimental work has
documented the quantum reflection and diffraction of He atoms, dimers, trimers
and Neon atoms when reflected from a grating. Conditions for the observation of
emerging beam resonances have been discussed and measured. In this paper, we
provide a theoretical simulation of the quantum reflection in these cases from
a grating. We confirm, as expected the universal dependence on the incident de
Broglie wavelength only of the threshold angles for the observation of emerging
beam resonances. However, the angular dependence of the reflection
efficiencies, that is the ratio of scattered intensity into specific
diffraction channels relative to the total intensity is found to be dependent
on the specifics of the incident particle. The dependence of the reflection
efficiency on the identity of the particle is intimately related to the fact
that the incident energy dependence of quantum reflection depends on the
details of the particle surface interaction.
