NMR Study of the Chemisorption Bond of Carbon Monoxide on Platinum

The authors report ¹³C NMR studies of ¹³CO adsorbed on small Pt particles and show that the data yield quantitative information about the CO-Pt bond. They find that the ¹³C resonance position is shifted 200 ppm to higher frequency than in CO gas. They prove that the shift arises from polarization of the electron spins in the bond (a Knight shift) by showing that the spin-lattice relaxation obeys the Korringa law. Using ESR results from CO radicals, they deduce the local density of states of the CO 5σ orbital on the carbon atom at the Fermi energy. The NMR also reveals diffusion of CO on the Pt surface.