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  • 1
    Call number: PIK Q 200-99-0362
    In: ZIB-Report SC
    Type of Medium: Monograph available for loan
    Pages: 11 p.
    Series Statement: ZIB-Report SC 99-12
    Branch Library: PIK Library
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  • 2
    Call number: PIK Q 200-00-0047
    In: ZIB-Report SC
    Type of Medium: Monograph available for loan
    Pages: 28 p.
    Series Statement: ZIB-Report SC 99-11
    Branch Library: PIK Library
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  • 3
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The water solubility in haplogranitic melts (normative composition Ab39Or32Qz29) coexisting with H2O-H2 fluids at 800 and 950 °C and 1, 2 and 3 kbar vapour pressure has been determined using IR spectroscopy. The experiments were performed in internally heated pressure vessels and the hydrogen fugacity (f H2) was controlled using the double capsule technique and oxygen buffer assemblages (WM and IW). Due to the limited lifetimes of these oxygen buffers the water solubility was determined from diffusion profiles (concentration-distance profiles) measured with IR spectroscopy in the quenched glasses. The reliability of the experimental strategy was demonstrated by comparing the results of short- and long-duration experiments performed with pure H2O fluids. The water solubility in Ab39Or32Qz29 melts equilibrated with H2O-H2 fluids decreases progressively with decreasing f H2O, as f H2 (or X H2) increases in the fluid phase. The effect of H2 on the evolution of the water solubility is similar to that of CO2 or another volatile with a low solubility in the melt and can be calculated in a first approximation with the Burnham water solubility model. Recalculation of high temperature water speciation for AOQ melts coexisting with H2O-H2 fluids at 800 °C, 2 kbar suggests that the concentrations of molecular H2O are proportional to f H2O (calculated using available mixing models), indicating Henrian behaviour for the solubility of molecular H2O in haplogranitic melts.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1546-170X
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] Recently developed major histocompatibility complex (MHC) multimer technologies allow visualization and isolation of antigen-specific T cells. However, functional analysis and in vivo transfer of MHC multimer-stained cells is hampered by the persistence of T-cell receptor (TCR)–MHC ...
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 6365-6366 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Based on structure calculations of small ethylene (C2H4)n clusters published previously [R. Alrichs et al., Z. Phys. D 15, 341 (1990)], shifts and splittings of the fundamental excitation frequency of the ν7 mode are calculated for the dimer, trimer, and tetramer. Using a first order perturbation approach, we find blue shifts in the order of 1–3 cm−1 which compare well with experimental findings. It is shown that the shifts are approximately independent of the cluster size and of the isomeric structure (ringlike or chainlike) of the ethylene complexes.
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 9410-9424 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A method for predicting splittings and shifts of bands in infrared spectra of small clusters of polyatomic molecules is presented. Based on an approach of early publications of Buckingham, the influence of the intermolecular forces on the vibrational energy levels of the constituent molecules is calculated using perturbation theory to second order. In order to describe the interaction of identical molecules, this ansatz is extended to also cover degenerate systems. In first order, a coupling of the vibrational modes of the interacting molecules occurs which leads to delocalized vibrations of all the molecules in the cluster. The second order correction of the vibrational excitation frequencies are found to be dominated by the intramolecular couplings of the normal modes due to the cubic anharmonicity of the force field. The procedures developed here are applied for the interpretation of vibrational photodissociation spectra of small methanol clusters in the region of the fundamental excitation frequency of the OH stretching mode (ν1, 3681.5 cm−1), the CH3 rocking mode (ν7, 1074.5 cm−1), and the CO stretching mode (ν8, 1033.5 cm−1). Using semiempirical models for the intermolecular potential functions, splittings and positions of the experimental bands can well be explained. The nonequivalent positions of the two molecules in the linear dimer structure give rise to two different absorption frequencies for each of the three modes of the donor and the acceptor molecule, respectively. The trimer and tetramer spectrum with only one absorption band are in agreement with the existence of symmetric planar ring structures (C3h and C4h) for these species. The pentamer spectrum which also consists of one band is explained by the occurrence of three closely spaced frequencies of an asymmetric ring. The double peak structure in the hexamer spectra can be attributed to a distorted ring structure of S6 symmetry, while the occurrence of other energetically near-degenerate isomers can be ruled out by means of their spectra.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 343-355 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The role of solvent effects in association reactions is studied in atom-cluster collisions. Classical trajectory studies of the systems H+Cl(Ar)n (n=1,12) are used to investigate the influence of size, structure, and internal energy of the "microsolvation'' on the H+Cl association reaction. The following effects of solvating the chlorine in an Arn cluster are found. (1) In the H+ClAr system there is a large "third body'' effect. The single solvent atom stabilizes the newly formed HCl molecule by removing some of its excess energy. The cross section found at low energies is a substantial fraction of the gas-kinetic cross section. The molecule is produced in highly excited vibrational-rotational states. (2) Some production of long-lived HCl...Ar complexes, with lifetimes of 1 ps and larger, is found for the H+ClAr collisions. Weak coupling stemming from the geometry of the cluster is the cause for long life times. These resonance states decay into HCl+Ar. (3) At low collision energy (E=10 kJ/mol) for H+Cl(Ar)12, the H+Cl association shows a sharp threshold effect with cluster temperature. For temperatures T≥45 K the cluster is liquidlike, and the reaction probability is high. For T≤40 K the cluster is solidlike, and there is no reactivity. This suggests the potential use of reactions as a signature for the meltinglike transition in clusters. (4) At high collision energies (E=100 kJ/mol) H atoms can penetrate also the solidlike Cl(Ar)12 cluster. At this energy, the solid–liquid phase change is found not to increase the reaction probability.
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  • 8
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The Floquet-based quantum-classical Liouville equation (F-QCLE) is presented as a novel theoretical model for the interaction of molecules with intense laser pulses. This equation efficiently combines the following two approaches: First, a small but spectroscopically relevant part of the molecule is treated quantum-mechanically while the remaining degrees of freedom are modeled by means of classical molecular dynamics. The corresponding nonadiabatic dynamics is given by the quantum-classical Liouville equation which is a first-order approximation to the partial Wigner transform of full quantum dynamics. Second, the dynamics of the quantum subsystem is described in terms of instantaneous Floquet states thus eliminating highly oscillatory terms from the equations of motion. The resulting F-QCLE is shown to have a well defined adiabatic limit: For infinitely heavy classical particles and for infinitely slow modulation the dynamics adiabatically follows the Floquet quasi-energy surfaces for a strictly time-periodic field. Otherwise, nonadiabtic effects arise both from the motion of the classical particles and from the modulation of the field which is assumed to be much slower than the carrier frequency. A numerical scheme to solve the F-QCLE is based on a Trotter splitting of the time evolution. The simplest implementation can be realized by an ensemble of trajectories stochastically hopping between different Floquet surfaces. As a first application we demonstrate the excellent agreement of quantum-classical and fully quantum-mechanical dynamics for a two-state model of photodissociation of molecular fluorine. In summary, due to the favorable scaling of the numerical effort the F-QCLE provides an efficient tool for the simulation of medium to large molecules interacting with intense fields beyond the perturbative regime. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Experimental investigations were carried out in spray scrubbers of different sizes with cocurrent flow of gas and liquid. Of special interest were the local processes in the mass transfer zone. The scrubber was operated with warm water/air system (cooling tower) to obtain detailed information about mass transfer. Air is being humidified with water vapour, which in turn leads to a temperature drop in the liquid. The liquid temperatures are relatively easy to measure and are shown as liquid isotherms. In the case of plug flow, the liquid isotherms should be straight horizontal lines. In reality, significant deviations from plug flow are caused by the transfer of liquid to the walls. A large part of the liquid forms a film flow at the wall. Furthermore, nearly all the mass transfer is completed in the zone of liquid atomization immediately beneath the nozzle. The number of measured transfer units was between 0.5 and 2.0 and was significantly influenced by the liquid flow rate. Based on the improved knowledge of the proceses inside the scrubber, a simplified model has been developed. Since the model simulates all the essential processes inside the mass transfer zone, liquid distribution and mass transfer efficiency can be approximately predicted.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 13C-NMR. spectra of one natural and ten semi-synthetic cannabinoids were analyzed in detail. Assignments of the signals are based on their chemical shifts, splitting patterns in 1H-off-resonance decoupling experiments and comparison with 13C-NMR. data of related cannabinoids. With some compounds final assignments were made by selective 1H-decoupling experiments and incremental calculations.
    Additional Material: 1 Tab.
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