Charge transfer effects on CO bond cleavage: CO and potassium on Fe(100)

Abstract

The effects of submonolayer coverages of potassium on CO chemisorption on the Fe(100) surface has been studied with TPD, XPS, and He I and He II UPS. Thermal desorption experiments show an increased capacity of the surface to hold dissociated CO and a lowering of the energy barrier to dissociation. The weakly bound molecular CO states (α 1 and α 2) showed increased activation energies for desorption with increasing potassium coverage. However, the more strongly bound π-CO state (α 3) desorbs at a lower temperature with increasing potassium coverage. XPS data indicate that chemisorbed potassium on the clean Fe surface is bound in a semi-metallic state; not a fully ionic form. CO coadsorption partially oxidizes the chemisorbed potassium via a charge transfer mechanism. Potassium TPD data along with the K, C, O core level shifts demonstrate the formation of a K x O surface complex upon CO dissociation.