The structure of the local Co(II) six-ring oxygen environment in zeolite A and the corresponding ligand field spectrum have been studied using large cluster models, including all six surrounding Si or Al tetrahedra terminated by either H or OH groups. Structures were optimized by means of density functional theory (DFT), using a nonlocal (BP86) approach and keeping the orientation of all dangling bonds frozen at the X-ray diffraction (XRD) positions. Electronic spectra were calculated using multiconfigurational perturbation theory based on a CASSCF wave function (CASPT2). It is shown that, in all cases, the presence of the Co(II) ion induces a local distortion of the zeolite surface, resulting in an oxygen coordination number of 3, 4, or 5, depending on the Si/Al ratio. This distortion is reflected in the calculated electronic spectra, showing an increased splitting of the Co2+ free-ion 4F and 4P states as compared to the (average) XRD structures. A new general assignment of the spectrum is proposed, different from earlier assignments based on ligand field theory. The calculated excitation energies of the optimized structures are in excellent agreement with the experimental band positions, thus proving the strength of the present combined DFT−CASPT2 approach. Our results further suggest that the experimentally observed splitting of the main band in the spectrum is due to the presence of asymmetric coordination sites, rather than to Jahn−Teller effects or spin−orbit coupling. The latter may, however, at least partly be responsible for the splitting of the weak feature at 25 000 cm-1.

The fluctuations in the zero-field splitting (ZFS) of the electronic ground state of the Ni(II) ion in aqueous solution have been studied through a combination of ab initio quantum chemistry calculations, including spin–orbit coupling, and molecular dynamics (MD) simulations. The ab initio calculations for the hexa-aquo Ni(II) complex have been used to generate an expression for the ZFS as a function of the distortions of the idealized Th symmetry of the complex along the normal modes of Eg and T2g symmetries. The MD simulations provide a 200 ps trajectory of motions in the system consisting of a Ni(II) ion and 255 water molecules, which is analyzed in detail in terms of both the structure and the dynamics in the solvation sphere around the ion. The time correlation function (TCF) for the ZFS interaction has been computed and analyzed. It is found that the mean square amplitude of the ZFS is about 5.2 cm−1, which is about twice the estimates based on the model-dependent analysis of the proton spin relaxation in the aqueous Ni(II) solution. The decay of the ZFS TCF is found to occur on a subpicosecond time scale, which is much faster than earlier proposals. It is also interesting to note, for comparison with theoretical models, that the ZFS tensor is far from cylindrical and that the normal modes of Eg och T2g symmetry both contribute to its fluctuations.

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The conditions for preparing selective surfaces by combinations of absorber-reflector tandems are discussed. The optical constants for Fe2O3, Cr2O3, CuO and Cu2O have been measured and the possibility of preparing selective surfaces based on these, and some related oxides, on steel- and copper-substrates has been investigated.

Reflectance measurements on eleven grades of stainless steel have been performed. It is found that the metallurgical phase is a more important parameter for the reflectance behavior than the detailed content of the alloying elements. The optical constants for one austenitic and one ferritic grade have been calculated by the Kramers-Krönig analysis. For the extrapolation, a fitting procedure to the results from measurements with polarized light at 10° and 60° incidence was used. The austenitic steels have a higher reflectance than the ferritic and martensitic, but their integrated solar reflectance of 68% is considered too low for solar reflectors. Two of the natural oxides on stainless steel, Fe2O3 and Cr2O3, have been studied as separate films, and their optical constants determined by combined transmission and reflectance measurements. The metal and oxide results are combined in an evaluation of the optical selectivity that can be obtained with oxidized stainless steel surfaces. It is concluded that a ferritic steel base is to be preferred because of its lower reflectance. Assuming perfect boundary layers and using conventional interference calculations it is found that Fe2O3 gives better selectivity than Cr2O3 since both the first interference minimum and maximum will be lower in that case.