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UV-Vis reflectance studies of H2 adsorption and CO/H2 interaction at MgO and CaO surfaces
No full textCO adsorption on MgO and CaO: Spectroscopic investigations of stages prior to cyclic anion formation
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UV-diffuse reflectance spectra of ammonia adsorbed on alkaline earth oxides and analogy with charge-transfer-to-solvent spectra
No full textAn experimental and theoretical evaluation of surface states in MgO and other alkaline earth oxides
No full textUltra-violet (u.v.) diffuse reflectance spectra of microcrystalline MgO, CaO, SrO and BaO reveal bands at energies below those of bulk excitonic transitions. Correlation of the spectra permit three distinctive absorptions (I, II, III) to be identified, each with similar characteristics in the respective oxides. The absorptions are ascribed to surface states, and the transitions have the characteristics of excitons. Excitons II and III obey the Mollwo-Ivey relation typical of bound excitons, but excition I with the highest energy of transition behaves similarly to a free exciton of the bulk. The four oxides are isostructural and ionic. The Levine-Mark theory of the surface states of ionic insulators, not hitherto tested for oxides, is examined. The numerical values of the parameters appropriate to the oxides are evaluated by using experimental data on bulk excitons. It is shown that the theory accounts satisfactorily for the energies of exciton I in MgO, CaO and SrO on the basis that it is an excitation of a surface anion located on a cube face of the crystal (fivefold coordination). Excitons II and III can only be tentatively assigned, but they are attributed to surface ions in fourfold and threefold coordination, respectively, the ions being at steps, edges or kink sites rather than on low-index faces, and thereby having a similar character to bulk excitons bound at internal lattice imperfections. The increased covalency shown by ions in low coordination prevents the application of the Levine-Mark theory
Surface properties of alkaline earth oxides as studied by UV-visible diffuse reflectance spectroscopy
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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