| Abstract
| - The adsorption of CO on Mo(100) has been calculated for several adsorption states at four surface coveragesusing density functional theory (DFT). Dissociation of CO on Mo(100) has been investigated for two surfacecoverages: 0.25 and 0.5 monolayer (ML). A full analysis of the vibrational frequencies of CO was performed,to determine whether structures are stable adsorption states or transition states. Results show that CO adsorbsmolecularly on the Mo(100) surfaces up to coverages of 0.5 ML at 4-fold hollow sites with the molecularaxis tilted away from the surface normal by 55−57° and dissociates easily with activation energies rangingfrom 0.45 to 0.56 eV, leading to energy gains of −1.71 and −0.59 eV at 0.25 and 0.5 ML, after dissociation,respectively. The adsorption energy of the CO molecule at 0.25 ML is −2.64 eV with a C−O stretchingvibration of 1062 cm-1. Increasing the CO surface concentration leads to a lower C−O stretching frequencyof 958 cm-1, which is remarkable, and it is in conflict with the Blyholder model and previous experimentalobservations for CO on transition-metal surfaces. Furthermore, calculations reveal that reported CO desorptionpeaks in literature, thought to be due to recombination of carbon and oxygen, are more likely due to moleculardesorption of CO at the 4-fold hollow position with a tilted geometry. This conclusion is supported by thelow recombination energies calculated (one-third of that described in literature).
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