CO INTERACTION WITH ULTRATHIN MGO FILMS ON A MO(100) SURFACE STUDIED BY INFRARED REFLECTION ABSORPTION-SPECTROSCOPY, TEMPERATURE PROGRAMMED DESORPTION, AND X-RAY PHOTOELECTRON-SPECTROSCOPY

The interaction of CO with MgO ultrathin films grown on a Mo(100) surface is studied using infrared reflection-absorption spectroscopy, temperature programmed thermal desorption (TPD), and x-ray photoelectron spectroscopy. CO adsorbed on 7 ML of MgO shows an infrared band at 2178 cm-1. This blue-shift of the CO stretching frequency relative to that of CO in the gas phase (2143 cm-1) is attributed to electron charge transfer from the CO 5-sigma orbital to the MgO surface. It is further shown that CO adsorption induces a 0.4 eV shift in the Mg(2p) and O(1s) core levels of the MgO thin films to lower binding energy, consistent with the charge transfer from CO molecules to the MgO thin films. The TPD spectra indicate that CO molecules on the MgO thin films desorb in the 100-180 K sample temperature range. The CO adsorption heat on 7 ML of MgO is deduced to be 9.9 kcal/mol using an isothermal adsorption method.