COVERAGE AND SITE DISTRIBUTION EFFECTS IN THE DESORPTION OF CARBON-MONOXIDE FROM SULFUR-COVERED NI(100)

Static and time resolved Fourier transform infrared spectroscopic studies were combined with threshold temperature programmed desorption studies to examine the effects of adsorbed sulfur on the kinetics of CO desorption from Ni(100). The appearance of new desorption states upon the addition of sulfur to Ni(100) can be attributed to the occupation of four-fold hollow and modified bridge-bonded species produced by the presence of sulfur. The observed kinetics of desorption from these surfaces is very sensitive to the initial binding site distribution of the adsorbed CO. Adsorbing at 100 K without anneal leads to a reduction in the measured desorption energy, except at the highest sulfur coverages studied. Apparently, relaxation of the adsorbed phase from a nonequilibrium distribution among sites on the surface during temperature programmed desorption is incomplete, leading to stronger repulsive interactions on the average and reduced desorption energies following adsorption at low temperature.