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1993[X]
61Author    M. A. Coplan, J. H. Moore, J. A. TossellRequires cookie*
 Title    (e, 2 e)-Spectroscopy and the Electronic Structure of Molecules. A Short Review with Selected Examples  
 Abstract    The simple plane wave target Hartree-Fock impulse approximation for the (e, 2e) reaction is developed. One result of the approximation is the separation of the expression for the (e, 2e) cross-section into a kinematic factor and a structure factor that contains all of the information about the target. When the target is a molecule, the structure factor can be further separated into atomic terms and a geometric term. This is illustrated for a simple one-electron homonuclear diatomic molecule. Three examples of the application of (e, 2e) spectroscopy to systems of chemical interest are given. They are borazine (inorganic benzene), the methyl siloxanes and the inorganic complex trimethylamine boron trifluoride. 
  Reference    Z. Naturforsch. 48a, 358—370 (1993); received January 30 1992 
  Published    1993 
  Keywords    (e, 2e)-Spectroscopy, Electron momentum spectroscopy, Electron momentum density, Electronic structure 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0358.pdf 
 Identifier    ZNA-1993-48a-0358 
 Volume    48 
62Author    Erich WeigoldRequires cookie*
 Title    Recent Advances in Electron Momentum Spectroscopy  
 Abstract    The flexibility of the (e, 2e) technique or "electron momentum spectroscopy" (EMS) in obtaining information on the electronic structure of atoms, molecules, and solids is demonstrated. High-resolution EMS measurements for argon, including the first measurements of momentum profiles belonging to the 2 P° and 2 D e -manifolds, are used to demonstrate the technique for atomic targets. The d-wave transitions in argon are entirely due to initial-state correlations. The first (e, 2e) measure-ments on an excited target, and also on an oriented target, are discussed. Sodium atoms are pumped to the m, = +1 state of the excited 3p-state by cr + -light from a laser. The (e, 2e) measurements on this excited state are in excellent agreement with the momentum density given by the 3p (m, — 1) Hartree-Fock wavefunction. The recent measurements of the valence-electron momentum distribu-tions for ethyne, as well as some earlier results for water, are used as an example of the application of EMS to the study of molecules. The application of the EMS technique to measure spectral momentum densities in condensed-matter targets is demonstrated by some recent results on amor-phous carbon. 
  Reference    Z. Naturforsch. 48a, 371—389 (1993); received March 28 1992 
  Published    1993 
  Keywords    Electron momentum densities, Electron momentum spectroscopy, Wavefunction map-ping, Binding energies 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0371.pdf 
 Identifier    ZNA-1993-48a-0371 
 Volume    48 
63Author    M. Peter, T. Jarlborg, A. A. Manuel, B. Barbiellini, S. E. BarnesRequires cookie*
 Title    What Can Positrons Contribute to High-Tc Superconductivity?  
 Abstract    The positron annihilation technique has made well-known contributions to the study of Fermi surfaces in "classical" superconductors, including A15 phases where the definition of the Fermi surface has been questioned on the grounds of Anderson localization. In the case of the supercon-ducting oxides, even more far out models were proposed, which made the clear imaging of the Fermi surface by positrons desirable. The difficulties due to the predicted weakness of the signal, and the large possibility for trapping have now been surmounted and the Fermi surface has been seen; what more can we learn from positrons? After presenting the actual situation with experiment, we will comment on enhancement and correlation and their effect on ACAR and lifetime studies. Then we explain the picture of Jarlborg and Singh of enhancement, with its recent tests for many substances. We conclude by asking the question of sensitivity of positrons to many-body effects. Ferromagnetism, antiferromagnetism, possibly charge density waves have been seen -superconductors, heavy fermions and spinons-holons would pose a problem. Stephan Berko (1924-1991) was interested in these problems and knew that better machines and better detectors would open new possibilities. 
  Reference    Z. Naturforsch. 48a, 390—397 (1993); received December 12 1991 
  Published    1993 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0390.pdf 
 Identifier    ZNA-1993-48a-0390 
 Volume    48 
64Author    L. C. Smedskjaer, A. BansilRequires cookie*
 Title    Positron Annihilation Studies of the Electronic Structure and Fermiology of High-Tc Superconductors  
 Abstract    We discuss the application of the positron annihilation angular correlation (ACAR) spectroscopy for investigating the electronic structure and Fermiology of high-T c superconductors, with focus on the YBa 2 Cu 3 O v system where most of the experimental and theoretical work has to date been concentrated. Detailed comparisons between the measured 2 D-ACAR positron spectra and the corresponding band theory predictions show a remarkable agreement (for the normal state), indicat-ing that the electronic structure and Fermi surface of this material is described reasonably by the conventional picture. 
  Reference    Z. Naturforsch. 48a, 398—405 (1993); received January 25 1992 
  Published    1993 
  Keywords    Positron annihilation, Angular correlation of annihilation radiation (ACAR), Electron momentum density, High-T c superconductors 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0398.pdf 
 Identifier    ZNA-1993-48a-0398 
 Volume    48 
65Author    T. SpringerRequires cookie*
 Title    High-Resolution Neutron Spectroscopy for the Investigation of Hydrogen Diffusion and Molecular Rotations in Solids  
 Abstract    An introductory survey on applications of high-resolution neutron spectroscopy is presented, dealing with the motion of hydrogen in solids, namely concerning (i) random rotational motions or stationary tunneling states of NH 4 -ions or CH 3 -groups, and (ii) diffusion of hydrogen in alloys. For the rotation of hydrogenous groups in solids, at higher temperatures rotational jumps can be found, whereas quantum states are observed by |J.eV-spectroscopy at temperatures below 50 K. On the other hand, hydrogen diffusion does not reveal pronounced evidence of quantum effects, except for hydrogen in a metal containing impurity atoms. 
  Reference    Z. Naturforsch. 48a, 406—414 (1993); received January 7 1992 
  Published    1993 
  Keywords    Quasielastic neutron scattering, Diffusion, Tunneling 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0406.pdf 
 Identifier    ZNA-1993-48a-0406 
 Volume    48 
66Author    RalphO. SimmonsRequires cookie*
 Title    Single-Particle Momentum Distributions from Deep Inelastic Neutron Scattering (DINS)  
 Abstract    Single-particle longitudinal momentum distributions in condensed matter are now accessible to direct measurement using eV neutrons. Some systems of particular interest include a) quantum solids and fluids, formed from "Hie, 4 He, and H 2 , b) prototype molecular crystals, formed from noble gases, c) fluids such as H 2 and Ne, which show deviations from classical behavior and d) mixed systems, in which guest-host interactions may be important. Quantum solids can be investigated at substan-tially different densities, for different structures, and further, can be compared to the corresponding fluids, with which they have significant similarities in their single-particle properties such as their momentum distributions. Noble gas solids comprise a graduated family with progressively varying importance of zero-point energy, of phonon anharmonicity, and of multi-body forces. They have also been very useful for matrix isolation studies, and eV neutron scattering can yield their center-of-mass motions, not previously seen directly. Finally, noble gas fluids can be used to investigate the nature and extent of final-state effects in the neutron scatttering. Such effects are defined to be the difference between the longitudinal "neutron Compton profile" and the longitudinal momentum distribution. 
  Reference    Z. Naturforsch. 48a, 415—424 (1993); received December 27 1991 
  Published    1993 
  Keywords    Momentum distribution, Dynamics, Neutron scattering 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0415.pdf 
 Identifier    ZNA-1993-48a-0415 
 Volume    48 
67Author    AlanC. Evans, Jerry Mayers, DavidN. Timms, K. Malcolm, J. CooperRequires cookie*
 Title    Deep Inelastic Neutron Scattering in the Study of Atomic Momentum Distributions  
 Abstract    The electron-volt spectrometer (EVS) at the pulsed neutron source facility (ISIS) is being devel-oped for the study of atomic momentum distributions. Neutrons with energies in the range 1 to 100 eV are incident on the sample, and the time-of-flight (TOF) spectrum of the scattered beam is measured by an array of fixed detectors. A resonant foil difference technique is used to yield a set of TOF spectra for those neutrons scattered into a fixed energy and through fixed angles. Informa-tion on the momentum distribution of the target nuclei can be deduced within an impulse approx-imation in a procedure analogous to that in Compton scattering of electrons by photons. Crystalline compounds containing aligned hydrogen bonds and other hydrogenous compounds are of particular interest owing to the high cross-section of the proton at these neutron energies. With improved statistical accuracy of the data it is anticipated that deviations of the proton's potential from a harmonic potential may be determined. Non-hydrogenous systems have also been investi-gated. A description is given of the basic theory and interpretive method. Data obtained on numer-ous systems are presented and discussed. 
  Reference    Z. Naturforsch. 48a, 425—432 (1993); received December 3 1991 
  Published    1993 
  Keywords    Compton profile, DINS, Neutron momentum 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0425.pdf 
 Identifier    ZNA-1993-48a-0425 
 Volume    48 
68Author    R. C. Blasdell, D. M. Ceperley, R. O. SimmonsRequires cookie*
 Title    Neutron and PIMC Determination of the Longitudinal Momentum Distribution of HCP, BCC and Normal Liquid 4 Het  
 Abstract    Deep inelastic neutron scattering has been used to measure the neutron Compton profile (NCP) of a series of condensed 4 He samples at densities from 28.8 atoms/nm 3 (essentially the minimum possible density in the solid phase) up to 39.8 atoms/nm 3 using a chopper spectrometer at the Argonne National Laboratory Intense Pulsed Neutron Source. At the lowest density, the NCP was measured along an isochore through the hep, bcc, and normal liquid phases. Average atomic kinetic energies are extracted from each of the data sets and are compared to both published and new path integral Monte-Carlo (PIMC) calculations as well as other theoretical predictions. In this prelimi-nary analysis of the data, account is taken of the effects of instrumental resolution, multiple scatter-ing, and final-state interactions. Both our measurements and the PIMC theory show that there are only small differences in the kinetic energy and longitudinal momentum distribution of isochoric helium samples, regardless of their phase or crystal structure. 
  Reference    Z. Naturforsch. 48a, 433—437 (1993); received December 27 1991 
  Published    1993 
  Keywords    Momentum distribution, Neutron, Helium 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0433.pdf 
 Identifier    ZNA-1993-48a-0433 
 Volume    48 
69Author    M. A. Fradkin, S.-X Zeng, R. O. SimmonsRequires cookie*
 Title    Deep Inelastic Neutron Scattering Studies of Atomic Momentum Distributions in Condensed Argon and Neon  
 Abstract    Using deep inelastic neutron scattering, direct measurements have been made, i) of the dynamic structure factor of a series of condensed argon samples over the temperature range 18 to 85 K, near melting (for wave-vector transfers 12 to 26 Ä -1) and ii) of liquid neon, near 27 K (for wave-vector transfers 10.4 to 27.6 Ä -1). Neutron time-of-flight chopper spectrometers were employed. Single-particle kinetic energies, <£ k >, can be obtained from the analysis of the Doppler-broadened recoil spectrum of the target particles. For argon the temperature dependence of <£ k > can be compared to expectations from theory, from thermodynamic data, and from previous neutron scattering measurements on collective vibrational modes. For liquid neon the wave-vector-transfer dependence of J{y), the longitudinal momentum distribution function, is being analyzed for final-state effects. 
  Reference    Z. Naturforsch. 48a, 438—442 (1993); received December 23 1991 
  Published    1993 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0438.pdf 
 Identifier    ZNA-1993-48a-0438 
 Volume    48 
70Author    C. H. Rüscher, M. Zimmermann, M. GötteRequires cookie*
 Title    Investigations of the Anisotropic Optical Reflectivity of Binary and Ternary Nb-W Oxides Possessing Block-Type Crystal Structure  
 Abstract    We have studied the anisotropic optical properties of binary Nb0 2 5 _ a (0 < Ö < 0.083) and ternary Nb 18 _ £ W 8+£ 0 6? (e = 0,1,..., 9) compounds using the polarized regular-reflection method. We observed strong anisotropic behaviour for all reduced phases. The anisotropic effect can be related to the crystallographical structure principle and to the doping of charge carriers by the reduction of oxygen (<5) or substitution of W for Nb (e) in the binary and ternary oxides, respectively. Our results indicate that the charge carriers are confined to the structural block units. For increasing 3 and e, metal-like properties occur (<5 > 0.1, e > 8) in the infinite block direction only. 
  Reference    Z. Naturforsch. 48a, 443—446 (1993); received December 31 1991 
  Published    1993 
  Keywords    Optical reflectivity, Block-type crystal structure, Niobium oxide, Niobium tungsten oxide 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0443.pdf 
 Identifier    ZNA-1993-48a-0443 
 Volume    48 
71Author    Reinhard HoneggerRequires cookie*
 Title    On Heisenberg's Uncertainty Principle and the CCR  
 Abstract    Realizing the canonical commutation relations (CCR) [N, 0] = — i as N = — i d/d9 and 0 to be the multiplication by 9 on the Hilbert space of square integrable functions on [0, 27t], in the physical literature there seems to be some contradictions concerning the Heisenberg uncertainty principle (AN) (A0) > 1/4. The difficulties may be overcome by a rigorous mathematical analysis of the domain of state vectors, for which Heisenberg's inequality is valid. It is shown that the exponentials exp {it N} and exp{is0} satisfy some commutation relations, which are not the Weyl relations. Finally, the present work aims at a better understanding of the phase and number operators in non-Fock representations. 
  Reference    Z. Naturforsch. 48a, 447—451 (1993); received August 20 1992 
  Published    1993 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0447.pdf 
 Identifier    ZNA-1993-48a-0447 
 Volume    48 
72Author    Th Halm, W. Hoyer, H. Neumann, R. BellissentRequires cookie*
 Title    Determination of Partial Structure Factors of Molten Eutectic Ni 33 Ge 67  
 Abstract    Using isotopic substitution and X-ray scattering, different weighted structure factors were mea-sured and combined in order to calculate partial structure factors. Although we got an overdeter-mined system of equations, the solution of this problem was difficult due to the small value of the determinant. From the partial pair correlation functions and the radial concentration correlation function a splitting of the first coordination shell is obvious. The dip in S Ni _ Ge and the corresponding peak in S Ni _ Ni indicate some degree of charge transfer in the melt. 
  Reference    Z. Naturforsch. 48a, 452—456 (1993); received January 18 1993 
  Published    1993 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0452.pdf 
 Identifier    ZNA-1993-48a-0452 
 Volume    48 
73Author    Z. DonkóRequires cookie*
 Title    A Study of the Motion of High-Energy Electrons in a Helium Hollow Cathode Discharge  
 Abstract    The motion of high-energy electrons was studied in a helium hollow cathode discharge using Monte Carlo simulation. The calculations were carried out in the pressure range of 2-10 mbar. The length of the cathode dark space (CDS) was determined by simulation in an iterative way using experimental voltage-current density characteristics of the discharge. At the lowest helium pressure (2 mbar) the concentration of high-energy electrons was found to be the same at the CDS-negative glow boundary and at the midplane of the discharge while at 8 mbars it was found to be by 1-2 orders of magnitude smaller. The results of our calculations support the existence of "oscillat-ing" electrons. The probability of 1, 2 and 3 transfers through the negative glow (NG) for primary electrons was found to be 37%, 11 % and 2%, respectively, at 2 mbar pressure. The spatial distribu-tion of ionizations and the angular distribution of electron velocity at the CDS-NG boundary were also investigated. The pressure dependence of the current balance at the cathode was obtained, and the results indicate that with decreasing pressure other secondary emission processes than ion impact become important in the maintenance of the discharge. 
  Reference    Z. Naturforsch. 48a, 457—464 (1993); received November 23 1992 
  Published    1993 
  Keywords    Hollow cathode discharge, Electron energy distribution, Monte Carlo simulation, Oscillating electrons, Current balance 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0457.pdf 
 Identifier    ZNA-1993-48a-0457 
 Volume    48 
74Author    V. M. Chhaya, J. J. Tarwadi, Smita ChhagRequires cookie*
 Title    Elastic Scattering of Electrons by Helium Atoms at Intermediate Energies  
 Abstract    The unitarised Eikonal Born series (UEBS) method has been used successfully by Byron et al. for elastic scattering of electrons and positrons by hydrogen atoms. Here an attempt is made to apply the UEBS method in the case of elastic scattering of electrons by helium atoms. The total and differential cross sections are calculated for the energy range 100-700 eV. The results are compared with experimental and other theoretical results. It is found that the results obtained with the UEBS method agree best with the experimental results. 
  Reference    Z. Naturforsch. 48a, 465—468 (1993); received November 21 1992 
  Published    1993 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0465.pdf 
 Identifier    ZNA-1993-48a-0465 
 Volume    48 
75Author    Slawomir BugajskiRequires cookie*
 Title    On Classical Representations of Convex Descriptions  
 Abstract    It is demonstrated that if V* is not a vector lattice, where V is a base norm Banach space, then there is no commutative observable providing a classical representation for V. This observation generalizes a similar result of Busch and Lahti, obtained for V -the trace class of operators on a separable complex Hilbert space. 
  Reference    Z. Naturforsch. 48a, 469—470 (1993); received November 3 1992 
  Published    1993 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0469.pdf 
 Identifier    ZNA-1993-48a-0469 
 Volume    48 
76Author    Alarich WeissRequires cookie*
 Title    Approaches to the Study of van der Waals Interactions in Solids  
 Abstract    Van der Waals forces are of short range. In molecular crystals the interacting atoms or groups of atoms of a molecule are fixed in their position with respect to the atoms of the neighboring molecules. From measurements of the intermolecular interactions via properties which can be assigned to the individual atoms (groups), such as hyperfine interactions or vibrational frequencies, as a function of the intermolecular distances, the van der Waals (vdW) potentials may be evaluated. We propose the use of discrete changes of intermolecular distances for studying vdW-interactions, the method of "Several Solid States", a) by combining a molecule A with different moleculs B, in stoichiometric proportions and in a crystallographically ordered way to molecular solid complexes; b) by investigating the changes of atomic (group) properties in systems with two ore more solid phases appearing in the phase diagram as a function of temperature (pressure). This way of using several solid states is offered only by chance; c) by using the fact that in many molecular solids there is more than one molecule in the asymmetric unit of the elementary cell in the crystal structure, and therefore several vdW-potentials for chemically identical intermolecular neighbors; d) by the synthesis of compounds containing the atoms (groups), the vdW-interactions of which one wants to study, with one or more centers of chirality. With one center of asymmetry in the molecule one finds the molecule considered in two different situations of vdW-contacts at least, and, in first approximation, one can assume identical intramolecular interactions (besides the optical activity). Two chirality centers within the molecule lead to three (at least) different crystal fields: a) (±); b) () respectively (+ +); c) (, + +). Examples of hyperfine interaction studies, based on this "Several Solid States" concept are discussed. 
  Reference    Z. Naturforsch. 48a, 471—477 (1993); received January 4 1993 
  Published    1993 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0471.pdf 
 Identifier    ZNA-1993-48a-0471 
 Volume    48 
77Author    Reha Basaran, Shi-Qi Dou, Alarich WeissRequires cookie*
 Title    Crystal Structures and 35 C1 NQR Spectra of the Metastable and the Stable Phase of Guanidinium bis-Monochloroacetate, [C(NH 2 ) 3 ]®[(ClH 2 C)COOH *** OOC(CH 2 Cl)l e  
 Abstract    From acid aqueous solutions of guanidinium carbonate and monochloroacetic acid, (ClH 2 C)COOH :H 2 NC(= NH)NH 2 ^2.5, the compound [C(NH 2) 3 ] e [(ClH 2 C)COOH • • • OOC(CH 2 Cl)] e crystallizes with the space group C^-Pl, Z = 4, a = 1147.4 (5) pm, b= 1113.2 (5) pm, c = 876.5 (4) pm, a = 88.66 (2)°, 0 = 80.31 (2)°, y = 84.41 (2)° (metastable phase I). Cooled to 77 K once, phase I transforms at room temperature slowly into the stable phase II, orthorhombic, D^ — Pbca, Z = 8, a= 1299.2 (4) pm, b= 1533.7 (4) pm, c= 1073.9 (3) pm. The crystal structure determinations show for both phases an ionic lattice with guanidinium cations [C(NH 2) 3 ]® and acid bis-(monochloroacetate) anions [(ClH 2 C)COOH • • • OOC(CH 2 Cl)] e in which a monochloroacetic acid molecule and a monochloroacetate ion are bound to the dimer anion by an asymmetric hydrogen bond O-H • • • O. A strong crystal field effect, much dependent on temperature, is observed in the 35 C1 NQR quadruplet spectrum of phase I, with a frequency spread of «4 MHz at 300 K, whereas in phase II the frequency splitting of the observed 35 C1 NQR doublet is almost constant between 77 K and 310 K, about 700 kHz. The phase transition I -+ II is very sluggish and unidirectional. The transition II —»-1 needs the recrystallization of II from water. Structure and dynamics of the two solid phases are discussed. 
  Reference    Z. Naturforsch. 48a, 478—490 (1993); received January 4 1993 
  Published    1993 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0478.pdf 
 Identifier    ZNA-1993-48a-0478 
 Volume    48 
78Author    Shi-Qi Dou, Reha Basaran, Helmut Paulus, Alarich WeissRequires cookie*
 Title    Crystal Structure and 35 C1 NQR of ( —) /?-(trichloromethyl)-/?-propiolactone. Comparison with (± ) /?-(trichloromethyl)-/?-propiolactone  
 Abstract    The crystal structure of(—)/?-(trichloromethyl)-/?-propiolactone at room temperature is reported, as is the 35 C1 NQR spectrum in the range 77 ^ T/K ^ 323.5. The compound crystallizes with the space group D*-2 1 2 1 2 lt Z = 8, a = 2416.0 (10) pm, b = 975.6 (4) pm, c = 595.0 (2) pm. The intra-molecular distances and angles of the two crystallographically independent (-) molecules in the unit cell are equal within the limits of error. The spread of the 3 *C1 NQR spectrum is within 600 kHz, not changing in the temperature range covered. The crystal structure and 35 C1 NQR spectrum are discussed. The results found for the (-) compound are compared with the corresponding ones reported for the (+) compound [1], and the influence of the different intramolecular interactions in the two solid states of the chemically identical compounds on the NQR spectrum is discussed. 
  Reference    Z. Naturforsch. 48a, 491—496 (1993); received January 4 1993 
  Published    1993 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0491.pdf 
 Identifier    ZNA-1993-48a-0491 
 Volume    48 
79Author    AnnaLisa Maniero, Antonio Toffoletti, Carlo CorvajaRequires cookie*
 Title    ENDOR Spectra of 2-Methyl-Naphthalene-TCNB Triplet Trap in Naphthalene-TCNB Single Crystals  
 Abstract    Naphthalene-TCNB charge transfer crystals doped with 2-methyl naphthalene illuminated by visible light give rise to triplet traps which have been identified by EPR and ENDOR spectroscopy as 2-methyl naphthalene-TCNB CT complexes in their first excited triplet state. The complete hyperfine tensors of all the 2-methyl naphthalene protons have been obtained by analysis of the variation of the ENDOR frequencies with the crystal orientation in the magnetic field. The structure of the CT complex, the spin distribution and the CT character are discussed. 
  Reference    Z. Naturforsch. 48a, 497—504 (1993); received November 30 1992 
  Published    1993 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0497.pdf 
 Identifier    ZNA-1993-48a-0497 
 Volume    48 
80Author    Uwe HohmRequires cookie*
 Title    Frequency-and Temperature-Dependence of Second Refractivity Virial Coefficients  
 Abstract    A reasonable heuristic extrapolation of a theory given by Buckingham is used to estimate the frequency-and temperature-dependence of the second refractivity virial coefficient. The calculations are carried out for the atoms He, Ne, Ar, Kr, Xe and the small molecules H 2 , N 2 , 0 2 , HCl, C0 2 , N 2 0, NH 3 , CH 4 , C 2 H 4 , and SF 6 . In some cases the frequency-dependence of B R (co, T) is compared with experimental values, showing sometimes considerable deviations between experiment and the heuristic approach used in this work. 
  Reference    Z. Naturforsch. 48a, 505—513 (1993); received December 14 1992 
  Published    1993 
  Keywords    Refractive index, Refractive index virial coefficient, Polarizability 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0505.pdf 
 Identifier    ZNA-1993-48a-0505 
 Volume    48 
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