The Adsorption and Co-Adsorption with CO of NO on Cu(110) Studied with EELS and LEED

Abstract

The adsorption of NO on Cu(110) and its interaction with co-adsorbed CO at a crystal temperature of 80 K have been investigated with EELS. Dissociation of NO occurring at higher temperatures or higher exposures has been studied with both EELS and LEED. For exposures of less than 1.2 Langmuir of ¹⁴NO at a crystal temperature of 80 K, vibrational energies are initially observed at 106, 195, and 262 meV with EELS. With increasing NO coverage, the first peak reaches a maximum intensity and then diminishes while the second peak grows. However, both peaks vanish for exposures greater than 1.2 Langmuirs. If the crystal is heated above 113 K both peaks also vanish. The third peak, which represents the CO stretching vibration of less than 5 % of a monolayer of CO, shifts upward in energy with increasing NO coverage but does not shift back when the first two peaks vanish. Hence, the NO or its products do not desorb under these conditions. With higher exposures of NO followed by heating to 500 K a distinct loss peak at 49 meV associated with O_ad in the long bridge site is observed. No additional vibrational peak is observed for nitrogen. However, a comparison of LEED patterns produced following NO and O adsorption at 80 K followed by annealing to 500 K indicates that N_ad is also present. By using the isotopic energy shifts obtained by adsorbing ¹⁵NO, the two low exposure peaks are assigned to the bending and stretching modes of adsorbed NO, respectively. Since the intensity of the bending mode peak is greater initially than the stretching mode, it is concluded that the NO is initially adsorbed in a strongly bent configuration. Co-adsorption with 0.25 monolayer of CO results in a substantial suppression of the bending mode and energy shifts in both the CO and NO stretching vibrations.

Research sponsored by the Division of Materials Science, U.S. Department of Energy under contract W-7405-eng-26 with Union Carbide Corporation.