A quantum-chemical study of the adsorption of water, formaldehyde and ammonia on copper surfaces and water on ZnO(0001)

The chemisorption of H 2 O, H 2 CO and NH 3 on Cu surfaces and of H 2 O on ZnO(0001) is examined employing semiempirical quantum-chemical calculations (INDO/S) and clusters of limited size ( Cu n , n = 14, 16, 18; Zn m O m , m = 10). The present results combined with our previous results for H 2 CO and NH 3 on ZnO(0001) indicate that upon adsorption on Cu surfaces and on ZnO(0001), water, formaldehyde and ammonia are electron donors. Most of the transfer of charge from the molecules toward the surfaces is from the lone pairs: the 3a 1 MO in NH 3 , the 3a 1 and 1b 1 MO's in H 2 O, and the 2b 2 MO in H 2 CO. H 2 CO is a σ-donor and a π-acceptor when adsorbed on Cu surfaces. In the cases of H 2 O and NH 3 , the contribution of the LUMO of the free molecule to the chemisorption bond is negligible. In contrast, for H 2 CO, a contribution of the 2b 1 (π) orbital (LUMO) to the Cu surface-molecule bond is observed. The bond order indices indicate that the 4s and 4p orbitals of the metal (Cu or Zn) are primarily responsible for the chemisorption bond of H 2 O, H 2 CO and NH 3 on copper and on zinc oxide surfaces. The influence of chemisorption effects upon the NH bond orders of NH 3 , the CO and CH bond orders of H 2 CO, and the OH bond orders of H 2 O are discussed. Based on these INDO/S results, the UPS spectra of H 2 O, NH 3 and H 2 CO on Cu surfaces and of H 2 O on ZnO(0001) are discussed and compared with experimental results.