SUCCESSIVE POPULATION OF SUBSURFACE AND SURFACE SITES UPON HYDROGEN CHEMISORPTION ON 1X2-RECONSTRUCTED PT(110)

He-diffraction measurements and intensity analyses based on close-coupled channels calculations show that the repulsive potential corrugation amplitude ζm = 1.5 A ̊ of missing-row Pt(110)1 × 2 increases to 2.0 Å upon saturating the stronger bonded β2-H chemisorption state without change of the attractive potential. We conclude that β2-H occupies sites below the topmost Pt rows, whereby the initial ∼ 15% inward relaxation changes into ∼ 20% outward relaxation. A pronounced decrease of the corrugation amplitude at higher coverages signals population of deep trough sites upon filling of the β1-H adstate. © 1990.