THE EFFECT OF SURFACE PASSIVATION ON ROTATIONALLY INELASTIC-SCATTERING - N(2) SCATTERED FROM W(110), W(110)-(2X2)N, W(110)-(1X1)H, AND PT(111)

The effects of surface reactivity on rotationally inelastic scattering has been examined by comparing the scattering of N2 from the reactive W(110) surface and from the passivated N and H reconstructions, W(110)-(2x2)N and W(110)-(1 X 1)H, as well as the nonreactive Pt(111) surface. The translational energy, rotational state population distributions, and angular momentum alignment of N2 scattered from these surfaces have been measured as a function of incident energy E(i), incident angle theta(i), and exit angle theta(f). The trends in the final translational and rotational energy correlate well with the average atomic mass of each surface. However, some of the greater rotational excitation for N2 scattered from W(110) compared to W(110)-(1 X 1)H can be attributed to a more anisotropic potential with respect to initial molecular orientation for N2-W(110) compared to N2-W(110)-(1 X 1)H or N2-Pt(111). The rotational distributions indicate that parallel momentum is not conserved for N2 Scattered from W(110) or from W(110)-(2x2)N, but that parallel momentum is partially conserved for N2 scattered from W(110)-(1X1)H. Furthermore, measurements of angular momentum alignment show that significant in-plane forces are present, and that these forces are due to the repulsive part of the N2-surface potential of each system. The results are consistent with the N2-W(110) potential being highly corrugated with respect to both initial molecular orientation and impact parameter and with this corrugation being reduced dramatically by passivating the surface with the adsorption of hydrogen.