CHEMISORPTION ON RHENIUM - N2 AND CO

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.