Interaction between chemisorbed N_2 and Li promoter atoms: A comparison between the stepped Ru(109) and the atomically smooth Ru(001) surfaces

摘要

We present a direct side-by-side comparison of the interaction of Li atoms and N_2 molecules on the atomically stepped Ru(109) single crystal surface and on the atomically smooth Ru(001) single crystal surface using infrared reflection absorption spectroscopy (IRAS) and temperature programmed desorption (TPD). At low adsorbate coverages there is spectroscopic evidence for the formation of a Li_x(N_2)_y complex on the Ru(109) surface, whereas no such complex is observed on the Ru(001) surface. This complex is due to local interactions between an adsorbed Li atom and N_2 adsorbed on the atomic steps of Ru(109). The short range interaction near the atomic steps is characterized by the development of several highly red-shifted v(N_2) modes in the region of ～2130cm~(-1) in the IR spectra. Adsorbed N_2 molecules on both Ru(109) and Ru(001) also are influenced by the long range electrostatic field produced by Li adsorbate atoms, causing a red shift in the uncomplexed N_2 species, which monotonically increases as the Li coverage in increased. On the Ru(001) surface, small coverages of N_2 influenced by the long range effect of Li are initially chemisorbed parallel to the surface resulting in the absence of infrared activity. In addition we have also found that Li does not cause N-N bond scission on Ru(001) below 250 K.