Diffraction and rotational transitions of D-2 from NiAl(110) have been measured at incident energies between 88 and 157 meV. The measurements were done along the [1 (1) over bar0] azimuth and using a set up which allows the recording of diffraction patterns at a fixed angle of incidence. Elastic first-order diffraction and rotationally inelastic diffraction peaks were observed over the whole incident energy range explored. The elastic diffraction data could be fitted using the simple Eikonal approximation only over a very narrow range of incident energies. Similarly, a Debye-Waller-type attenuation of diffraction intensities as a function of surface temperature was only verified at low incident energies (similar to100 meV). The absolute 0-->2 transition probability was found to increase from 10 to 20% in the energy range investigated, whereas the one corresponding to the 2-->0 transition remained constant at 10%. An important conclusion of our work is that the behavior exhibited by these two transitions as a function of incident energy is independent of angle of incidence.