Group IVA chemisorption on metals

Carbon chemisorption on metals has been studied on the substrates Ni(100), Mo(100) and Zr(1000), Although studies of atomic C chemisorption are few, the resulting structures are diverse and are tabulated in table 7. 

Of these three systems, C on Ni 100) forms a p4g-c(2x2)-2C overlayer by inducing an unusual reconstruction of the substrate (see fig. S). In the Ni(100)p4g-c(2x2)-2C structure, the C adatoms occupy equivalent hollow sites in which the adjacent 4 Ni atoms in the top substrate layer undergo a clockwise rotation about the adsorbate. The second Ni layer is buckled by 0,15 A with the Ni atoms directly below the C adatom being pulled out of the surface. There is a significant expansion of the top layer spacing induced by C adsorption. There are two relevant Ni-C bond lengths in this structure. The Ni-C distance between the adatom and the top layer Ni atoms is 1.82 0.03 A, the distance between the adatom and the second layer Ni atom directly underneath is 1.95 0.03 A. This latter distance may be compared to the sum of the covalent radii of Ni and C which is 1.92 A. 

C adsorption on the open Mo(100) surface results in conventional hollow site adsorption in which the shortest C-Mo distance is between the adatom and the second layer Mo atom directly below the adsorption site. This C-Mo bond length, 1.99 0.05 A, is significantly shorter than the C-Mo distance between the adatom and top-layer Mo atoms 2.27 0.03 A. The sum of the covalent radii of C and Mo is 2.07 A. 

C adsorption on Zr(1000) involves the occupation by C of octahedral interstitial sites halfway between the first and second Zr layers. The resulting structure resembles that of bulk ZrC which involves the insertion of the C 

Schematic illustration of the Ni(100)-p4g-c(2x2)-2C reconstruction. Note the rotational reconstruction of the substrate indicated by the arrows, 

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