Chemisorption on Rhenium: N2 and CO

Abstract

The chemisorption of N₂ and CO on polycrystalline Re has been studied using flash desorption. A number of binding states have been identified and their binding energies have been estimated kinetically. Isotopic mixing between chemisorbed species has been observed for the β‐N₂ and β‐CO states on Re; there appears to be no evidence for dissociation of β‐CO. The γ‐N₂ and two α‐CO states on Re desorb without isotopic mixing. In general, the distribution and properties of binding states for N₂ and CO on Re are remarkably similar to those found for these adsorbates on W. An enhancement in nitrogen adsorption on Re occurs upon electron impact (150 eV) on N₂(g). A new set of strongly bound states are produced which are distinct from the β‐N₂ states populated by adsorption of ground‐state N₂(g). A comparison of the sticking coefficients for N₂ and CO on Re is made, using two independent methods (uptake and isotopic mixing) over a wide temperature range. The sticking coefficient for N₂ on Re decreases markedly with increasing temperature; for CO on Re, there is little effect of temperature on the sticking coefficient. A discussion is presented of migration‐limited bimolecular kinetics at elevated temperatures in the chemisorbed layer.