BONDING OF ACETONE TO RH(111) AND THE EFFECT OF OXYGEN

The adsorption of acetone on the 111 surface of rhodium and on the sam e surface partially covered (0.25) with oxygen was studied using exten ded Huckel calculations with the tight-binding approach. It was found, in agreement with experimental work of Barteau and coworkers, that ac etone prefers to bind in a side-on eta(2) mode on Rh(111), forming str ong Rh-O and Rh-C bonds: while in the modified surface, Rh(111)-p(2x2) O, it coordinates end-on, in a eta(1) mode, through the oxygen atom. T he eta(2) coordination, involving a strong back donation of electrons from the surface to the adsorbate, leads to a more pronounced weakenin g of the internal bonds of acetone, activating it toward further react ion, On the other hand, the side-on bonding is achieved essentially th rough orbitals having oxygen lone pair character and therefore the C-O and C-C bonds of the molecule remain almost undisturbed. Desorption, rather than reaction, takes place.