Crystal structure and mixed-valence state in 1′,1‴-dibutylbiferrocenium triiodide

In 1′, 1‴-dibutylbiferrocenium triiodide crystals A show temperature-independent trapped-valence state, while crystals B show a valence-delocalization of the mixed-valence state. The mixed-valence states of both crystals are discussed in relation to their crystal structures. Address after October 1991: Department of Chemistry, Faculty of Science, Hiroshima University, Kagamiyama, Higashi-Hiroshima 724, Japan     

Mixed-valence states of 11, 1111-dialkyl- and 11, 1111-bis(methylbenzyl)biferrocenium triiodides

It was found that the packing of cations and anions influences the electronic structures of mixed-valence binuclear ferrocene derivatives. Temperature-dependence of the mixed-valence state of 1¹, 1¹¹¹-diisobutylbiferrocenium triiodide was observed in a crystalline state, whereas only a trapped-valence state was found in a dispersed state. The packing effect was also observed for a series of 1¹, 1¹¹¹-dialkyl- and 1¹, 1¹¹¹-bis(methylbenzyl)biferrocenium triiodides by means of ESR spectroscopy.     

Formation of hot hexafluorobenzene in the 193 nm photolysis

Time-resolved absorption spectra of hexafluorobenzene vapor have been observed with ArF laser (193 nm) excitation. The initial intermediate is postulated to be due to HFB2(S₀) (hot hexafluorobenzene, with internal energy of 639 kj/mol) because the transient spectrum can be simulated as part of the S₃(¹E_1u) ← S₀ transition at 3050 K.     

Hydrogenated crystalline silicon fabricated at low-substrate temperatures by reactive sputtering in He-H2 atmosphere

Crystallized films of silicon containing about 5 at.% of bonded hydrogen have been fabricated by reactive sputtering in He and H₂ atmosphere at low substrate temperatures below 250°C. The structure was investigated by X-ray diffraction, Raman scattering, infrared and visible absorption measurements. The infrared spectra show two or three sharp absorption peaks at the stretching vibrational region of Si-H. The processes of both sputtering and crystallization are strongly affected by the presence of H₂.     

Transformation of resonant Raman scattering into luminescence in CdxZn1−xTe mixed crystals: Time-resolved spectroscopy

We report an experimental study of time characteristics of secondary emission in Cd_xZn_1-xTe mixed crystals (x = 0.32) under resonant excitation with a picosecond dye laser. When the incident laser frequency is tuned on to the luminescence maximum of localized excitons, the decay curve of the intensity of “Raman-like” lines exhibits a single exponential decay. Off resonance, however, a short-lived component corresponding to Raman scattering appears in addition to the long-lived component. The intensity of the Raman component relative to that of the luminescence component increases with increase of the off-resonance frequency. From these temporal behaviors, we have found, for the first time, the transformation of resonant Raman scattering into luminescence in mixed crystals as a function of incident frequencies.     

Singletons and twistors

Singletons and twistors are unified from a group-theoretic point of view. In particular, singletons are described as the de Sitter analogue of twistors.     

Core-exciton spectra of AlxGa1−xAs studied with synchrotron radiation

Core-exciton spectra of Al_xGa_1?xAs have been measured in the photon-energy region from 19 to 27 eV by use of synchrotron radiation. The core-excitons associated with the Ga 3d core-hole and the conduction electron around the lowest L₆ and X₆ symmetry points are found to be coupled with each other through intervalley electron-hole interactions. Quantitative analyses have elucidated that intervalley Coulomb term is playing a dominant role for this coupling. Another higher energy doublet structure is interpreted as due to the transition from the Ga 3d core-levels to the rather flat region in the second lowest conduction band around the L₆ and L_{4, 5} symmetry points.     

Determination of trace metals in seawater by graphite furnace atomic absorption spectrometry with preconcentration on silica-immobilized 8-hydroxyquinoline in a flow-system

Summary A flow-system utilizing a miniature column packed with silica-immobilized 8-hydroxyquinoline (I-8-HOQ) was used for the preconcentration of Cd, Pb, Zn, Cu, Fe, Mn, Ni, and Co from seawater prior to their determination by graphite furnace atomic absorption spectrometry (GFAAS). Enrichment factors sufficient to permit the analysis of an open ocean seawater reference material using 50 ml sample volumes (100 ml for Co determinations) were obtained. Recoveries of the above elements from seawater averaged 93% (range 87–97%) with absolute blanks ranging between 0.04 ng (Ni) and 4.0 ng (Fe). Estimated detection limits for these elements vary from 0.2 ng l^–1 (Co) to 40 ng l^–1 (Fe) based on a 50 ml sample volume (100 ml for Co).

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Bestimmung von Spurenmetallen in Meereswasser durch Graphitofen-AAS mit Anreicherung an Kieselgel-immobilisiertem 8-Hydroxychinolin in einem Durchflu\system