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This paper presents a detailed study of a water adlayer adsorbed on Pt(111) and Rh(111) surfaces using periodic density functional theory methods. The interaction between the metal surface and the water molecules is assessed from molecular dynamics simulation data and single point electronic structure calculations of selected configurations. It is argued that the electron bands around the Fermi level of the metal substrate extend over the water adlayer. As a consequence in the presence of the water layer the surface as a whole still maintains its metallic conductivity-a result of a crucial importance for understanding the process of electron transfer through the water/metal interface and electrochemical reactions in particular. Our results also indicate that there exists a weak bond between the hydrogen of the water and the Rh metal atoms as opposed to the widespread (classical) models based on purely repulsive interaction. This suggests that the commonly used classical interactions potentials adopted for large scale molecular dynamics simulations of water/metal interfaces may need revision. Two adsorption models of water on transition metals with the OH bonds pointing towards or away of the surface are also examined. It is shown that due to the very close values of their adsorption energies one should consider the real structure of water on the surface as a mixture of these simple "up" and "down" models. A model for the structure of the adsorbed water layer on Rh(111) is proposed in terms of statistical averages from molecular dynamics simulations.

The reactivity and spectra of formaldehyde isomers and dimeric complexes between them are studied with ab initio methods. A large number of complexes between H2CO, trans-HCOH, cis-HCOH is calculated. Infrared and Raman spectra of (H2CO)2 are calculated with relatively simple methods using spectroscopic masses and scaled force constants. In this way, the structure of dimers in matrices can be deduced. Hydroxycarbene (HCOH) plays a key role in a model that explains a large number of experimental facts of the nonzero pressure photochemistry. Hydroxycarbene forms complexes with H2CO; the stabilization is due to classical hydrogen bonds. HCOH is a new example of an ambiphilic carbene. Addition products are formed from HCOH···H2CO complexes. The calculations show that, in agreement with matrix experiments, glycoaldehyde and methanol are easily formed. The formation of trans-HCOH occurs through a dimeric interaction with the shifting hydrogen. This bimolecular process is 9.6 kcal/mol (6–31G*) in favor of the unimolecular conversion. cis-HCOH might be formed via a nonplanar transition state, where also stabilization at the carbenic center is possible. When higher concentrations of HCOH are available, a hydrogen exchange mechanism easily transfers hydroxycarbene back to H2CO. Several experiments are suggested in this paper; notably, molecular beam and isotopic-mixture experiments will give useful information. The involvement of HCOH in the light-induced formose reaction is suggested.