A comparison of the interaction of CO, N2, and OC with Cu(100)

The cluster model approach has been used to compare the chemisorption properties, including vibrational frequencies (ωe) and dynamic dipole moments (e*), of C‐ and O‐bonded CO and N2 at an on‐top site of Cu(100). The binding energies and metal–adsorbate stretch ωe and e* are found to decrease in the order CO>N2>OC, with N2 expected to be bound and OC almost unbound; the metal–adsorbate bond distances and intra‐adsorbate stretch e* (including the sign) are in the opposite order, OC>N2>CO. While the C–O stretch frequency for C‐bonded CO is strongly reduced with respect to the free molecule, the frequencies for N2 and O‐bonded CO are found to be only slightly changed. The sequence in the strength of the interaction is explained by the different amount of metal‐to‐adsorbate charge transfer which is identified as the driving force behind the chemisorption process. Our theoretical results are compared with experimental data and the differences in the bonding of CO and N2 to transition metals are addressed.