Isotope effects on the rotationally inelastic diffraction dynamics of hydrogen scattered from Cu(001)

We investigate the rotationally inelastic diffraction (RID) of D-2(H-2) sca ttered from Cu(0 0 1) and discuss how isotope effects influence the RID pro babilities of D-2(H-2) by performing quantum dynamics calculations that inc lude all six degrees of freedom of D-2(H,). We show that the RID probabilit ies initially increase with increasing incident energies due to the activat ed nature of D2(H,) dissociation on Cu(0 0 1), which qualitatively agree wi th recent experimental RID peaks measured for D-2/Cu(0 0 1). Furthermore, c omparing the RID probabilities of D-2 and H-2, we observed strong isotope e ffects. Due to the small threshold energy of D-2 for rotational excitation and diffraction, as compared to H-2, the RID probabilities of D-2 are large r than those of H-2 in the low incident energy region. However with further increase in incident energies, the RID probabilities of D-2 become smaller than those of H-2. We conclude that this is a manifestation of the steerin g effect in the RID. (C) 2001 Elsevier Science B.V. All rights reserved.