Search results for "Alkali metal"
showing 10 items of 190 documents
Novel lithocholaphanes: Syntheses, NMR, MS, and molecular modeling studies
2007
Abstract Novel head-to-head lithocholaphanes 6 and 11 have been synthesized via precursors 1 – 5 and 7 – 10 with overall good yields, and characterized by 1 H, 13 C, and 15 N NMR spectroscopy, ESI-TOF mass spectrometry, thermal analysis, and molecular modeling. In addition, the binding abilities of 6 and 11 towards alkali metal cations have been investigated via competitive complexation studies using equimolar mixtures of Li + , Na + , K + , and Rb + -cations, and cholaphanes 6 and 11 . The formation of cation–cholaphane adducts was detected by ESI-TOF mass spectrometry. The trends in these comparative binding studies are nicely reproduced theoretically with PM3 energetically optimized stru…
Kinetics of correlated annealing of radiation defects in alkali halide crystals
1992
Abstract Kinetics of the correlated annealing of pairs of neutral (F-H) Frenkel defects in the KBr crystal is treated theoretically, taking into account defect diffusion, and annihilation at short distances stimulated by an elastic interaction. It is shown that an elastic interaction affects the annealing kinetics and the survival probability of close geminate detects considerably. The widespread description of the correlated annealing in terms of a first-order reaction fails for close defects yielding effective energies which in fact differ essentially from an activation energy of diffusion. Ea, even if it is corrected by an interaction energy. The effect of the initial distribution of def…
Properties of small clusters at ionic surfaces: (NaCl)nclusters (n=1–48) at the (100) MgO surface
1995
We have studied the geometry, binding energy, interaction with the surface, barriers for diffusion, optical absorption, and the possibility for their observation using atomic force microscopy of (NaCl${)}_{\mathit{n}}$ clusters (n=1--48) on the (100) MgO surface. We address the questions at which cluster size do the adsorbed molecules lose their identity and how do strained clusters accommodate the strain. The relation between the structure of initial molecular fragments adsorbed at the surface and the structure of the corresponding thick film is discussed. The results are compared with the calculated structures of the free clusters and the experimental data on the molecular-beam epitaxy of…
ChemInform Abstract: Interlocking Inorganic Screw Helices: Synthesis, Structure, and Magnetism of the Novel Framework Uranium Orthothiophosphates A11…
2010
<title>Shallow electron traps in alkali halide crystals: Mollwo-Ivey relations of the optical absorption bands</title>
2001
Evidences are given that two classes of the transient IR- absorption bands: (a) with max. at 0.27-0.36 eV in NaCl, KCl, KBr, KI and RbCl (due to shallow electron traps according G. Jacobs or due to bound polarons according E.V. Korovkin and T.A. Lebedkina) and (b) with max. at 0.15-0.36 eV in NaI, NaBr, NaCl:I, KCl:I, RbCl:I and RbBr:I (due to on-center STE localized at iodine dimer according M. Hirai and collaborators) are caused by the same defect- atomic alkali impurity center [M+]c0e- (electron e- trapped by a substitutional smaller size alkali cation impurity [M+]c0). The Mollwo-Ivey plots (for the transient IR-absorption bands) of the zero-phonon line energy E0 (for NaCl, KCl, KBr, Rb…
Energy transfer from colour centres to the dopant in alkali halides
1997
Abstract Energy transfer from F centres to the dopant ions in photostimulated processes is examined. It was found that in alkali halide systems the radiation defects are disposed in near vicinity of the dopants. Recombination of defects also takes place to a limited extent near the dopant with a fast and high-yield energy transfer to the latter. Role of unrelaxed H centres in the formation of donor-acceptor pairs is discussed. Some special exciton energy transfer mechanisms are analysed as well.
Analysis of self-trapped hole mobility in alkali halides and metal halides
2017
Support from Latvian National Research Program IMIS2 (2014–2017) and LZP Grant No. 237/2012 (2013–2016) is greatly appreciated.
Free and bound chlorophenols in kraft pulp bleaching effluents
1992
Abstract Free (F; hexane extractable) and chemically bound (B; alkali extractable) chlorophenols, catechols and guaiacols were measured from effluents of the C and E stages of chlorobleaching of kraft softwood pulp. Ratio B/F was in moste cases nearly one, but for tetrachloroguaiacol B/F was 20 in C and 2.70 in E stage. Organically bound chlorine (OCl) in chlorophenols was less than one percent of the total AOX (Adsorbable Organic Halogen) emitted.
Influence of temperature on the hydration products of low pH cements
2012
International audience; The chemical evolution of two hydrated "low pH" binders prepared from binary (60% Portland cement + 40% silica fume) or ternary (37.5% Portland cement +32.5% silica fume + 30% fly-ash) mixtures was characterized over one year at 20 degrees C. 50 degrees C, and 80 degrees C. The main hydrates were Al-substituted C-S-H. Raising the temperature from 20 to 80 degrees C caused a lengthening and cross-linking of their silicate chains. Ettringite that formed in pastes stored at 20 degrees C was destabilized. Only traces of calcium sulfate (gypsum and/or anhydrite) reprecipitated after one year in some materials cured at 50 degrees C and 80 degrees C. The sulfates released w…