| Abstract |
The chemical behavior of pyrimidine on the (0001) close-packed surface of a Ru single crystal was studied by reflection-absorption infrared spectroscopy (RAIRS) and by Hartree-Fock ab initio calculations. At 95 K, the spectra and theoretical simulations indicate molecular docking at fcc hollow sites, as a pi-complex almost parallel to the surface. With increasing coverage, some eta(4) on-top docked species appear, and for a highly packed monolayer physically adsorbed pyrimidine, with some preferential orientation induced by the chemically bonded species, is also present. Subsequent physisorbed layers, randomly oriented, form as exposure increases. The behavior of adsorbed species with thermal activation is not coverage dependent: annealing a low temperature packed monolayer induces rearrangements toward a denser pi-complex layer, at the expense of the other surface species, up to 130 K. At this temperature, a tilted intermediate and 2-pyrimidyl bonded to the surface by dehydrogenated C2 and one N, with loss of resonance, and oriented with the C-N bond tilted toward the surface are also proposed. 2-Pyrimidyl is stable between 130 and 180 K and starts desorbing or decomposing above this temperature. A multilayer formed at low temperature is stable up to 110 K and desorbs by annealing to 120 K. For higher temperatures, the composition of the surface layers is similar to that obtained from thermal activation of a dense monolayer. At 150 K, the surface adlayer has the same composition whether it results from an annealed low-temperature monolayer, an annealed multilayer, or a layer built above the stability limit of the multilayer. The relevance of the results obtained is based on the eventual extrapolation to the interactions of pyrimidinic ring molecules with ruthenium. |
