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991.
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994.
Giovanni Buffa Dr. Luca Dore Prof. Francesca Tinti Dr. Markus Meuwly Prof. 《Chemphyschem》2008,9(15):2237-2244
An experimental and theoretical study of pressure broadening and pressure shift of HCO+ rotational lines perturbed by collisions with He is presented. Results are reported from measurements at 88 K for the lines j=4←3, 5←4 and 6←5 with frequencies ranging from 0.35 to 0.54 THz. Using a new CCSD(T)/aug‐cc‐pVQZ potential energy surface for the He–HCO+ interaction, the collisional line shape parameters are studied from fully quantum and semiclassical calculations. Results from the quantum treatment are in satisfactory agreement with experiments whereas the semiclassical approach can lead to appreciable differences. A study of the dependence of line width Γ and shift s as a function of the translational energy shows the presence of quantum oscillations. Calculations on a previous Hartree–Fock‐based potential energy surface lead to quite similar results for the collisional line shape parameters. Using a simplified version of the potential morphing method it is found that the line width Γ is particularly sensitive to the long‐range part of the potential energy surface. This also explains the success of the first line‐broadening calculations which date back to the 1950s. 相似文献
995.
Barbara Platschek Dr. Ralf Köhn Dr. Markus Döblinger Dr. Thomas Bein Prof. 《Chemphyschem》2008,9(14):2059-2067
The structural evolution of periodic mesoporous material within the channels of anodic alumina membranes (AAMs) by evaporation‐induced self‐assembly (EISA) is investigated by a combination of in situ grazing‐incidence small‐angle X‐ray scattering (GISAXS) with parallel detection of solvent evaporation and ex situ transmission electron microscopy (TEM). Kinetically controlled and equilibrium‐controlled structural evolution can be distinguished for these EISA processes. A new mechanism for formation of mesostructures in the confined environment of AAMs is proposed. Data are presented for samples synthesized with nonionic surfactants at various surfactant:silica ratios and relative humidities. The formation of and transformations between circular or columnar 2D hexagonal and tubular lamellar structures are observed. The circular hexagonal phase is kinetically favored over the columnar hexagonal orientation. The TEM images provide evidence that phase transformations, depending on their type, either start preferentially at the channel wall or in the center of the mesostructured fibers. 相似文献
996.
Armbruster MK Weigend F van Wüllen C Klopper W 《Physical chemistry chemical physics : PCCP》2008,10(13):1748-1756
Efficient self-consistent field (SCF) schemes including both scalar relativistic effects and spin-orbit (SO) interactions at Hartree-Fock (HF) and density functional (DFT) levels are presented. SO interactions require the extension of standard procedures to two-component formalisms. Efficiency is achieved by using effective core potentials (ECPs) and by employing the resolution-of-the-identity approximation for the Coulomb part (RI-J) in pure DFT calculations as well as also for the HF-exchange part (RI-JK) in the case of HF or hybrid-DFT treatments. The procedures were implemented in the program system TURBOMOLE; efficiency is demonstrated for comparably large systems, such as Pb54. Relevance of SO effects for electronic structure and stability is illustrated by treatments of small Pb and Po clusters with and without accounting for SO effects. 相似文献
997.
Aine Desikusumastuti Thorsten Staudt Zhihui Qin Dr. Markus Happel Mathias Laurin Dr. Yaroslava Lykhach Dr. Shamil Shaikhutdinov Dr. Friedemann Rohr Dr. Jörg Libuda Prof. Dr. 《Chemphyschem》2008,9(15):2191-2197
Using scanning tunneling microscopy (STM), molecular‐beam (MB) methods and time‐resolved infrared reflection absorption spectroscopy (TR‐IRAS), we investigate the mechanism of initial NOx uptake on a model nitrogen storage and reduction (NSR) catalyst. The model system is prepared by co‐deposition of Pd metal particles and Ba‐containing oxide particles onto an ordered alumina film on NiAl(110). We show that the metal–oxide interaction between the active noble metal particles and the NOx storage compound in NSR model catalysts plays an important role in the reaction mechanism. We suggest that strong interaction facilitates reverse spillover of activated oxygen species from the NOx storage compound to the metal. This process leads to partial oxidation of the metal nanoparticles and simultaneous stabilization of the surface nitrite intermediate. 相似文献
998.
Braun J Fouqueau A Bemish RJ Meuwly M 《Physical chemistry chemical physics : PCCP》2008,10(32):4765-4777
Atomistic simulations are used to characterize the molecular dynamics (MD) of alkyl chains with different functionalizations in different water/acetonitrile mixtures (80/20 and 50/50). Starting from fully equilibrated solvent systems (flat density profile for both components), microheterogeneous structuring of the solvent in the chromatographic system is found for both mixtures. Depending on the functionalization of the alkyl chain (nitrile, amide, nitro, phenyl), differences in the density profiles of the two solvents (water/acetonitrile), the effective width of the stationary phase and the solvent gradients in the overlap region are observed. The solvent mixture (mobile phase) in RPLC is a liquid which is directly involved in the physical process and must be included explicitly. Far from the surface, the solvent displays bulk properties; closer to it the mixed solvent partitions due to the presence of the stationary phase. This creates a gradient in solvent strength perpendicular to the surface which influences the motions of the analyte. The surface is found to define the amount of water that can bind to it and defines its hydrophilic character. Proposals from the literature, such as the existence of persistent water filaments extending from the functionalized silica layer towards the bulk solvent, are discussed. Simulations of acridine orange near a -NH(2)- and -phenol-functionalized surface highlight the different dynamical behaviour (insertion vs. adsorption) of an analyte depending on the functionalization of the surface. 相似文献
999.
Antonietti M Niederberger M Smarsly B 《Dalton transactions (Cambridge, England : 2003)》2008,(1):18-24
The availability of well defined inorganic nanocrystals allows the construction of aligned structures with characteristic architectural elements in the nanometer range, the mesoscale. Contrary to alignment driven by external conditions and fields, we focus on strict "self-effects", where the organization is already encoded in the shape and mutual interaction potentials of the particles. This Perspective discusses the potential of this approach for generating valuable functional inorganic mesostructures. 相似文献
1000.
Talib J Green C Davis KJ Urathamakul T Beck JL Aldrich-Wright JR Ralph SF 《Dalton transactions (Cambridge, England : 2003)》2008,(8):1018-1026
Electrospray ionisation mass spectrometry (ESI-MS) and circular dichroism (CD) spectroscopy were used to compare the binding of mononuclear nickel, ruthenium and platinum complexes to double stranded DNA (dsDNA) and quadruplex DNA (qDNA). CD studies provided evidence for the binding of intact complexes of all three metal ions to qDNA. ESI mass spectra of solutions containing platinum or ruthenium complexes and qDNA showed evidence for the formation of non-covalent complexes consisting of intact metal molecules bound to DNA. However, the corresponding spectra of solutions containing nickel complexes principally contained ions consisting of fragments of the initial nickel molecule bound to qDNA. In contrast ESI mass spectra of solutions containing nickel, ruthenium or platinum complexes and dsDNA only showed the presence of ions attributable to intact metal molecules bound to DNA. The fragmentation observed in mass spectral studies of solutions containing nickel complexes and qDNA is attributable to the lower thermodynamic stability of the former metal complexes relative to those containing platinum or ruthenium, as well as the slightly harsher instrumental conditions required to obtain spectra of qDNA. This conclusion is supported by the results of tandem mass spectral studies, which showed that ions consisting of intact nickel complexes bound to qDNA readily undergo fragmentation by loss of one of the ligands initially bound to the metal. The ESI-MS results also demonstrate that the binding affinity of each of the platinum and ruthenium complexes towards qDNA is significantly less than that towards dsDNA. 相似文献