ADSORPTION OF NO ON PD(111)

The adsorption of NO on Pd(111) was studied by means of HREELS, LEED, UPS, TDS and ΔΦ measurements in the temperature range between 20 and 300 K. TDS results show that, after NO exposure at 100 K, desorption takes place from three desorption states (α,β and γ). The α state is characterized by a (2 × 2) structure and two pairs of loss energies at 35 and 60 meV (NO-Me) and 197 and 217 meV (N-O). On the contrary the γ state (no LEED pattern; 41 and 197 meV) and the β state (c(4 × 2); 39 and 200 meV) exhibit only one pair of losses as expected for a single adsorption site. Whereas, so far, all states have been assigned to a single bridge site, we argue that this may be correct for the β and γ but not for the α state for which we propose a mixture of a bridge and a shifted and/or tilted on-top site. At 20 K (NO)2 dimers are formed in the thick layer as characterized by HREELS and UPS. © 1990 Pergamon Press plc.