DISSOCIATIVE CHEMISORPTION OF NITROGEN ON RU(0001)

The dissociative chemisorption of nitrogen on clean and cesiated Ru(0001) surfaces has been studied using high-resolution electron energy loss spectroscopy (HREELS) and thermal desorption spectroscopy (TDS). N2 (at 300 K) chemisorbs dissociatively with a sticking coefficient of 2 X 10(-6), independent of substrate temperature which was varied between 420 and 700 K. The saturation coverage is found at 0.5 monolayer. The energy of the N-Ru stretching vibration is 71 meV at the bare surface and 69 meV at the cesiated Ru(0001) surface. The activation energy for desorption is about 190 kJ/mol for small coverages. The kinetic data suggest the existence of an activation barrier in the entrance channel of adsorption. Preadsorption of 0.08 monolayer of Cs increases the sticking coefficient only by a factor of 1.3, and the maximum amount of adsorbed N is reduced due to blocking of adsorption sites through Cs.