The kinetics of CO desorption from Ni(110)

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Abstract
The kinetics of CO desorption from clean Ni(110) have been measured by thermal desorption mass spectrometry (TDMS) using the method of variation of heating rates. Analysis of the desorption spectra gives the coverage dependence of the preexponential factor νd, and the activation energy Ed, of the desorption rate constant. For 0<θ<0.5, Ed is constant at 30.6 kcal/mol, allowing analysis of the coverage dependence of the preexponential factor under conditions where the compensation effect is absent. We observe only small changes in the preexponential factor under these conditions, where log[νd(s−1)] rises slowly from 14.6 to 15.3 from 0<θ<0.65. Near θ=0.8, a synchronous drop in νd by 0.6 orders of magnitude and in Ed by 5 kcal/mol is observed at the onset of formation of the (2×1)p2mg structure. These results are discussed in light of the structures of CO in Ni(110) and the effects of ordering transitions on the desorption kinetics. The experimental results for νd(θ) are compared with those predicted for desorption by three precursor mechanisms and for desorption of a lattice gas with lateral interactions.