ENDOTHERMIC DISSOCIATIVE CHEMISORPTION OF MOLECULAR D-2 ON AG(111)

The dissociative chemisorption of molecular D-2 On Ag is reported for the first time. Dissociation on the Ag(lll) surface is highly activated with an approximately exponential dependence on the energy of the incident molecules, the initial sticking probability increasing from approximate to 10(-7) at 230 meV to 10(-2) at 465 meV, for a beam incident along the surface normal. The sticking probability is sensitive to the internal temperature, or state distribution, of the D-2 beam, dissociative chemisorption being more efficient for higher vibrationally excited states. The threshold for dissociative chemisorption of the ground state lies at too high an energy to be accessed, indicating an activation barrier > 0.8 eV for dissociation of D-2(v = 0). Comparison with the activation barrier to D recombinative desorption of 0.28 eV indicates that dissociative chemisorption is endothermic. At large incidence angles and low nozzle temperatures adsorption is dominated by atoms formed in the nozzle, allowing an estimate of 0.6 for the initial sticking probability of D atoms at Ag(lll).