ADSORPTION, DESORPTION AND DISSOCIATION OF N2 ON W(110)

N2 adsorbs molecularly on W(110) at Ts ≤ 100 K with high and nearly constant sticking coefficient (s ≈ 0.7). Saturation coverage is estimated as N2/W = 0.7, from the p(4 × 1) LEED pattern seen at saturation and by analogy with CO adsorption. Desorption at ∼ 130-150 K seems to occur from more than a single binding state, even for partial coverages. The tightly bound component (75% of total N2 adsorbed, independent of coverage) desorbs with first-order kinetics as shown by isothermal measurements with E = 10.3 kcal, v = 1015 s-1. Approximately 10% of total N2 is converted to atomically bound N during desorption. The amount converted is independent of desorption temperature over the range 128-148 K, suggesting an activation energy equal to that of desorption of the tightly bound component, i.e. ∼ 10 kcal. This suggests that dissociation from preadsorbed N2 occurs via a different channel than dissociation from impinging energetic N2 molecules. © 1990.