HYDROGEN ADSORPTION SITE ON THE NI(110)-P(1 X 2)-H SURFACE FROM TIME-OF-FLIGHT SCATTERING AND RECOILING SPECTROMETRY (TOF-SARS)

The adsorption site of hydrogen on the Ni{110}-p(1 x 2)-H surface resulting from saturation exposure to H2 at approximately 310-350 K has been investigated by time-of-flight scattering and recoiling spectrometry (TOF-SARS). The recoiled neutral plus ion hydrogen atom flux resulting from 2-5 keV Ar+ or Ne+ pulsed ion beams incident on the surface was monitored as a function of crystal azimuthal angle and beam incidence angle. From classical trajectory calculations and shadowing and blocking analyses, it is concluded that hydrogen atoms are localized at the pseudo-three-fold sites on the (1 x 2) missing-row (MR) reconstructed Ni{110} surface; the (1x2) MR reconstruction is induced by hydrogen adsorption as shown elsewhere [Surf. Sci. 259 (1991) 253). Only the pseudo-three-fold site is consistent with all of the experimental data. The coordinates of the hydrogen adsorption site with respect to the nickel lattice were determined. The lateral distance of hydrogen from the 1st-layer Ni [110BAR] rows is 1.56 +/- 0.12 angstrom and the vertical distance above the substrate is 0.21 +/- 0.12 angstrom, providing Ni-H bond lengths of 2.0 angstrom to the two lst-layer Ni atoms and 1.5 angstrom to the 2nd-layer Ni atom.