We have incorporated the flexible RWK2 water potential into the parametrization of a chloride−water interaction potential from first principles calculations and used it to investigate the temperature effects in the infrared (IR) spectrum of Cl-(H2O)2. We have found that spectral signatures of hydrogen bonding between the two water molecules in the cluster disappear with increasing temperature, a consequence of the weak water−water interaction in the cluster.

We have performed direct measurements of the valence band structures of the light alkaline earth oxides BeO, MgO, and CaO using electron momentum spectroscopy (EMS). From these measurements, we have determined the band dispersions, valence bandwidths, and O(2s)–O(2p) intervalence bandgaps at the Γ point. For comparison we have also performed Hartree–Fock (HF) and density-functional (DFT) calculations in the linear combination of atomic orbitals (LCAO) approximation. Intervalence bandgaps compare reasonably well with the DFT calculations and previous experimental and theoretical studies. Our measured bandwidths, however, are significantly smaller. In particular, we find that contrary to conventional wisdom, the local density approximation of DFT overestimates the valence bandwidths of these ionic solids.

The electronic band structures of Be and BeO have been measured by transmission electron momentum spectroscopy (EMS). The low atomic number of beryllium and the use of ultrathin solid films in these experiments reduce the probability of electron multiple scattering within the sample, resulting in very clean "benchmark" measurements for the EMS technique. Experimental data are compared to tight-binding (LCAO) electronic structure calculations using Hartree-Fock (HF), and local density (LDA-VWN), gradient corrected (PBE) and hybrid (PBE0) density functional theory. Overall, DFT calculations reproduce the EMS data for metallic Be reasonably well. PBE predictions for the valence bandwidth of Be are in excellent agreement with EMS data, provided the calculations employ a large basis set augmented with diffuse functions. For BeO, PBE calculations using a moderately-sized basis set are in reasonable agreement with experiment, slightly underestimating the valence bandgap and overestimating the O(2s) and O(2p) bandwidths. The calculations also underestimate the EMS intensity of the O(2p) band around the Γ-point. Simulation of the effects of multiple scattering in the calculated oxide bandstructures do not explain these systematic differences.

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The chemisorption properties of carbon monoxide on two vicinal Ni(100) surfaces have been studied with surface infrared reflection–absorption spectroscopy and low energy electron diffraction. For coverages ≤0.50 monolayer, equilibrium adlayers are formed in which CO populates atop sites on the low-index (100) terrace, as well as twofold bridging sites along both the highly-kinked and close-packed step edges of the Ni[(100)-1.4°(01̄0)] and Ni[(100)-9°(01̄1̄)] surfaces investigated. Low energy electron diffraction (LEED) measurements confirm that all three long-range structures established on the (100) surface—c(2×2) at 0.50 ML, hexagonal at 0.61 ML, and compressed-hexagonal at 0.69 ML—are also formed on the Ni [(100)-1.4°(01̄0)] surface. On the Ni [(100)-9°(01̄1̄)] surface, however, only the ordered c(2×2) structure appears. A simple Arrhenius analysis of the relative population of step and terrace sites estimates a small binding energy preference for populating step sites. This weak preference is of comparable magnitude to the CO–CO interactions that produce long range structures. To evaluate quantitatively the binding energy difference between adsorption at step and terrace sites, step adsorption isotherms are measured as a function of total coverage at select temperatures over the 90–300 K window. The isotherms are modeled with simple Monte Carlo simulations of adsorption on stepped surfaces, which include a 1.0 kcal/mol binding energy preference for step sites. The data and simulations indicate that the primary role played by the steps in the chemisorption of CO is to serve as nucleation centers for island growth.