A molecular orbital analysis of the precursor state and the activation barrier for chemisorption. I. CO adsorbed on nickel (111)

The precursor state and the activation barrier for the associative chemisorption of carbon monoxide on nickel (111) has been investigated using semi-empirical molecular orbital (MO) calculations. Results show a weakly bound precursor state when CO is oriented parallel to the metal surface, and no precursor state for the perpendicular orientation. It is also shown that there is an activation barrier between the precursor and chemisorption states. The results are generally consistent with recent experimental observations of precursor-like states. A qualitative molecular orbital analysis is developed to explain the precursor state and the barrier for chemisorption.