Showing papers on "Quadrupole published in 1996"
TL;DR: Equal efficiencies can be reached simultaneously by adapting z-filter principles to MQMAS and to decrease dispersion signals in order to enhance the resolution using zNMR.
694 citations
TL;DR: Two highly stable and reproducible (87)Rb D(2)-saturated-absorption spectrometers at 780 nm are constructed using dither/third-harmonic lock-in detection and radio-frequency sideband techniques, respectively, and +/-3-kHz reproducibility and agreement are achieved.
Abstract: We have constructed two highly stable and reproducible (87)Rb D(2)-saturated-absorption spectrometers at 780 nm, using dither/third-harmonic lock-in detection and radio-frequency sideband techniques, respectively. We achieved +/-3-kHz reproducibility and agreement between these two independent systems. Heterodyne measurements of the hyperfine splittings of the 5P(3/2) state give its magnetic dipole (A) and electric quadrupole (B) hyperfine constants with a 10-fold reduction in uncertainty.
209 citations
TL;DR: In this article, a rotation-induced adiabatic coherence transfer (RIACT) was proposed to extract quantitative information about site populations from isotropic MQ NMR spectra.
Abstract: We describe a new approach for observation of multiple-quantum (MQ) NMR spectra of S = 3/2 nuclei with magic-angle spinning (MAS). The new method employs the Rotation-Induced Adiabatic Coherence Transfer (RIACT) that occurs between triple-quantum (3Q) and central-transition (1Q) coherences in S = 3/2 systems. In contrast to currently available coherence-transfer techniques, RIACT is relatively insensitive to the magnitude of the quadrupole interaction for e2qQ/h ≤ 4 MHz for both 3Q excitation and 3Q-to-1Q conversion. Thus, RIACT provides a means of extracting quantitative information about site populations from isotropic MQ NMR spectra. We illustrate the utility of the approach with 23Na (S = 3/2) MQ NMR spectra of a series of sodium salts exhibiting crystallographically distinct sites. The spectra provide quantitative measurements of quadrupolar parameters, chemical shifts, and relative site populations for each of the crystallographically distinct sodium sites.
191 citations
TL;DR: In this paper, a method for the effects of dipole and quadrupole polarizations on the interparticle interactions in molecular dynamics simulations is described, and the effect is to substantially improve the agreement with experiment of properties such as phonon dispersion and liquid structure relative to calculations with a simple pair potential.
Abstract: A method which allows for the effects of dipole and quadrupole polarizations on the interparticle interactions in molecular dynamics simulations is described. Multipole induction by both Coulombic and short-range interactions is included. The validity of a description of the interactions in condensed ionic systems with pair potentials supplemented with a description of polarization effects is assessed, and the implications for reliably parameterizing such a model are discussed. The role of cation quadrupole polarization is explored in simulations of solid and liquid AgCl. The effect is to substantially improve the agreement with experiment of properties such as phonon dispersion and liquid structure relative to calculations with a simple pair potential.
137 citations
TL;DR: In this article, the relativistic effects have been taken into account in the computations carried out with the help of two independent computer programs, SUPERSTRUCTURE (SST) and RELATIVISTIC HARTREE-FOCK (HFR).
Abstract: Radiative transition probabilities have been calculated for the magnetic dipole (M1) and electric quadrupole (E2) transitions connecting the 63 metastable levels in the 3d 6 4s, 3d 7 and 3d 5 4s 2 configurations in Fe II. The most important configuration interaction (CI) and relativistic effects have been taken into account in the computations carried out with the help of two independent computer programs, SUPERSTRUCTURE (SST) and RELATIVISTIC HARTREE-FOCK (HFR). The results obtained in the present work are compared with previous theoretical studies and with some astrophysical observations. The new data presented here are probably the most reliable to date.
106 citations
TL;DR: In this article, a rotational model for the core structure of one neutron halo nucleus is used to calculate the deformation parameter of the core and the charge to mass deformation ratio given by shell model calculations.
101 citations
TL;DR: In this article, a program for the computation of magnetic dipole and electric quadrupole diagonal (A J, B J ) and off-diagonal ( A J, J −1, B J,J −1, BJ, J −2 ) hyperfine interaction constants is described.
94 citations
TL;DR: In this paper, the orthogonally spin-adapted linear response coupled-cluster (LRCC) theory with singly and doubly excited clusters (CCSD) was employed to calculate quadrupole moment functions of the HF and N2 molecules in their ground electronic states.
Abstract: The orthogonally spin‐adapted linear‐response coupled‐cluster (LRCC) theory with singly and doubly excited clusters (CCSD) was employed to calculate quadrupole moment functions of the HF and N2 molecules in their ground electronic states. We also calculated several potential energy curves for both systems using various CC and non‐CC methods, ranging from the limited and full configuration interaction (CI) and first‐order CI (FOCI) to finite‐order many‐body perturbation theory. FOCI and related complete active space self‐consistent field (CASSCF) methods were used in both energy and quadrupole moment calculations. Most of the calculations were performed using the medium‐size basis set of TZ+2P quality devised by Sadlej [A. Sadlej, Coll. Czech. Chem. Commun. 53, 1995 (1988)] for high‐level ab initio calculations of electrostatic molecular properties. In addition, a number of model CC calculations using small basis sets were performed, for which the exact full CI results, both for the energy and multipole moments, are available. It was demonstrated that the CCSD approach provides a realistic description of quadrupole moment functions, for all relevant geometries in the case of HF and for internuclear separations up to 1.5 times the equilibrium bond length for N2. The results of this study will be used for the analysis of the rovibrational dependence of quadrupole moments and for the calculation of quadrupole transition moments for both HF and N2.
79 citations
TL;DR: In this paper, a new model of the solar magnetic activity cycle is proposed based on the symmetries of a rotating star, and describes the interaction between dipole and quadrupole fields in the weakly non-linear regime.
Abstract: A new model of the solar magnetic activity cycle is proposed. The model is based on the symmetries of a rotating star, and describes the interaction between dipole and quadrupole fields in the weakly non-linear regime. The model describes not only pure dipole and quadrupole dynamos, but also the transitions with increasing dynamo number to mixed polarity states, and in appropriate regimes to aperiodic states which are highly suggestive of prolonged activity minima such as the Maunder minimum.
74 citations
TL;DR: In this paper, the authors used the R-matrix method with a 49-term eigenfunction expansion for the dipole allowed (E1) and forbidden electric quadrupole and magnetic dipole (E2, M1) transitions in Fe III.
Abstract: Transition probabilities are obtained for both the dipole allowed (E1) ne structure transitions and the forbidden electric quadrupole and magnetic dipole (E2, M1) transitions in Fe III. For the E1 transitions, ab initio calculations in the close coupling (CC) approximation using the R-matrix method are carried out in LS coupling with a 49-term eigenfunction expansion for Fe IV. The ne structure components are obtained through algebraic transformation of the LS line strengths, and the oscillator strengths and A-coecients are computed using spectroscopic energies of the observed levels. Radiative transition probabilities for 9797 ne structure E1 transitions corresponding to 1408 LS multiplets among 200 bound states of Fe III are reported. Forbidden E2 and M1 transition probabilities are computed for 362 transitions among the 34 ne structure levels of all 16 LS terms dominated by the 3d 6 conguration using optimised conguration-interaction wavefunctions from the SUPERSTRUCTURE program in the Breit-Pauli approximation. Comparison of the present results is made with previous calculations and signicant dierences are found. Theoretical line ratios computed using the present E2 and M1 A-coecients show better agreement with observations for some prominent Fe III lines in the infra-red than those using the earlier data by Garstang (1957). This work is carried out as part of the Iron Project to obtain accurate radiative and collisional data for the Iron group elements. ?
72 citations
TL;DR: In this paper, Coulomb-excitation least-squares search code GOSIA was used to extract E2 matrix elements from the measured γ-ray yields, which were compared with the prediction of various collective models such as the asymmetric rigid rotor model, the γsoft model of Leander, and the IBA-2 model.
TL;DR: It is shown that lower concentration species can be effectively accumulated in the FTICR trapped ion cell, while the more abundant species are continually removed by the application of quadrupolar excitation in the form of band-limited or "colored" noise waveforms, ensuring "room" is made in the cell for lower abundance species, even during extended accumulation periods.
Abstract: Fourier transform ion cyclotron resonance (FTICR) mass spectrometry offers unparalleled analytical performance in most regards but has a dynamic range of typically no better than 102−103. This limitation reportedly arises from two opposing constraints, involving the maximum number of ions that can be effectively trapped (106−107) and the minimum number of ions required to produce a detectable signal (102−103). A potential solution to this dynamic range limitation is presented, based on the application of selected-ion accumulation using quadrupole excitation. We show that lower concentration species can be effectively accumulated in the FTICR trapped ion cell, while the more abundant species are continually removed by the application of quadrupolar excitation in the form of band-limited or “colored” noise waveforms. The result is that “room” is made in the cell for lower abundance species, even during extended accumulation periods. This approach was demonstrated with mixtures of the bovine proteins, insuli...
TL;DR: In this article, the magnetic dipole hyperfine interaction constant A for 297 energy levels with an uncertainty of between 0.2% and 3% was obtained for the Co I lines recorded by high-resolution Fourier Transform Spectrometry in the region 30000-2222 A.
Abstract: Most of the Co I lines recorded by high-resolution Fourier Transform Spectrometry in the region 3000–45000 cm−1 (30000–2222 A) show significant hyperfine Structure. Computer fits to 1020 of these line profiles have yielded values of the magnetic dipole hyperfine interaction constant A for 297 energy levels with an uncertainty of between 0.2% and 3%. The A Factors range from −0.0236 to +0.0598 cm−1 for the even levels, and from −0.03387 to +0.1028 cm−1 for the odd levels. For 208 of these A factors no previous measurements are known. Approximate values of the electric quadrupole hyperfine interaction constant B were found for 156 levels. These measurements of A and B factors allow, for the first time, correct allowance to be made for the effects of hyperfine structure in Co I both for abundance analysis and in the resolution of blended lines.
TL;DR: The possibility of retrieving parameters for the combined effect of quadrupole coupling and small chemical-shielding anisotropies from single-crystal NMR of the central transition for half-integer quadrupolar nuclei has been successfully investigated as discussed by the authors.
TL;DR: Advantages of the new ion guide include static rather than rf potential, low electrical noise, a large field-free region near the central axis of the guide, and simple mechanical construction.
TL;DR: The properties of both isoscalar and isovector monopole giant resonance (GR) are found to change drastically in nuclei around the neutron drip line.
Abstract: We study the effect of the unique shell structure as well as the very low particle threshold on collective modes in drip-line nuclei, first performing the Hartree-Fock (HF) calculation with Skyrme interactions and, then, using the random phase approximation solved in the coordinate space with the Green's function method. We examine also one-particle resonant states in the HF potential. The properties of both isoscalar and isovector monopole giant resonance (GR) are found to change drastically in nuclei around the neutron drip line. The characteristic feature of the isovector dipole modes as well as the isoscalar quadrupole modes in drip-line nuclei is also studied. \textcopyright{} 1996 The American Physical Society.
TL;DR: In this paper, the dipole polarizability of carbon tetrafluoride has been obtained from SCF and MP4 calculations, and the best values for the first hyperpolarizability are α = 19.51 e2a02Eh−1 and β = 6.0 e3a03Eh−2.
TL;DR: Cross-polarization/magic-angle spinning and rotational echo double resonance experiments involving two half-integer quadrupolar nuclei, 11B and 27Al, are reported, to demonstrate boron-aluminum connectivities in a model aluminoborate glass.
TL;DR: In this paper, the average steric orientation of D2 molecules desorbing from a Cu(111) surface was measured by laser-induced fluorescence with linearly polarized tunable vacuum ultraviolet radiation in the B1?u+(v',J',M')? X1?g+(v'',J'',M'').
Abstract: We report rotationally state-resolved measurements of the average steric orientation of D2 molecules desorbing from a Cu(111) surface. The desorbing flux of D2 molecules is probed by laser-induced fluorescence with linearly polarized tunable vacuum ultraviolet radiation in the B1?u+(v',J',M') ? X1?g+(v'',J'',M''). Molecules desorbing in the vibrational ground state show for all rotational states measured (J'' = 1 ? 8) a quadrupole alignment factor, A(2)0, compatible with a spatially isotropic distribution. A strong azimuthal, polar, and lateral corrugation of the dissociative interaction potential can cause this behavior.
TL;DR: In this article, the electric fields and potentials of an equilibrated assembly of ions and water molecules adjacent to a charged metal surface are calculated as a function of perpendicular distance z from the surface from data derived from molecular dynamics trajectories.
TL;DR: A theoretical explanation of the doubly shaped profiles of excitation spectra of Cs and Rb atoms in superfluid helium, with a model that the bubble structure of surrounding helium is not spherical, but is deformed instantaneously by a quadrupole oscillation.
Abstract: Our recent experiments show that the ${D}_{2}$ excitation spectra of Cs and Rb atoms in superfluid helium have doubly shaped profiles. Such line shapes are beyond the description of a simplified spherical atomic bubble model which explains properly general features of optical spectra of neutral atoms in liquid helium. This paper gives a theoretical explanation of the doubly shaped profiles, with a model that the bubble structure of surrounding helium is not spherical, but is deformed instantaneously by a quadrupole oscillation. The calculated energy level of the ${P}_{\frac{3}{2}}$ state of the deformed atomic bubble is split into two branches, giving the ${D}_{2}$ excitation line shape consisting of two components with different peak intensities and widths. The obtained line shape agrees qualitatively with the observed one, which enables us to confirm the importance of the dynamic Jahn-Teller effect due to a quadrupole oscillation of the atomic bubble surface induced by zero-point fluctuations.
TL;DR: The gravitational radiation produced by the coalescence of inspiraling binary neutron stars in the Newtonian regime is calculated using three-dimensional numerical simulations using the quadrupole approximation.
Abstract: We calculate the gravitational radiation produced by the coalescence of inspiraling binary neutron stars in the Newtonian regime using three-dimensional numerical simulations. The stars are modeled as polytropes and start out in the point-mass regime at wide separation. The hydrodynamic integration is performed using smooth particle hydrodynamics with Newtonian gravity, and the gravitational radiation is calculated using the quadrupole approximation. We have run a number of simulations varying the neutron star radii, equations of state, spins, and mass ratio. The resulting gravitational waveforms and spectra are rich in information about the hydrodynamics of coalescence, and show characteristic dependence on $\frac{\mathrm{GM}}{R{c}^{2}}$, the equation of state, and the mass ratio.
TL;DR: In this paper, the exact coefficients in the multipole potential expansion have been determined and a simple relationship is found for which certain key coefficients vanish, which enables immediate calculation of each higher order coefficient from a fixed set of values for the corresponding scaled coefficients.
TL;DR: In this article, a band-structure calculation based on the density functional theory has been performed for forsterite to obtain, with a parameter-free model, electric-field gradients for all nuclei.
Abstract: Ab initio band-structure calculations based on the density functional theory have been performed for forsterite to obtain, with a parameter-free model, electric-field gradients for all nuclei. Calculations based on the generalized gradient approximation yield the ratio of the largest components of the calculated electric-field gradients within 1% of the experimental value for 25Mg and within 2% of the experimental value for 170. The absolute values differ by about 5%, depending on which nuclear quadrupole moment is used in the conversion. The asymmetry parameters are also in good agreement with experimental data. Values obtained with a gradient-corrected exchange-correlation potential are better than those based on the standard local-density approximation. The calculated angles between the principal axes of the quadrupole coupling tensor and the crystallographic axes agree very well with the experimental data. For the Ml site the maximum deviation is 1.80, and for the M2 site the maximum deviation is 0.60. The current calculations allow an evaluation of three sets of experimental data for the 170 electric-field gradient. They also confirm a proposed assignment of the measured electric-field gradient tensors to specific 0 atoms.
TL;DR: In this article, a theoretical approach for the calculation of hyperfine parameters in solids from first principles is presented, which is based on the full potential linearized-augmented-plane-wave (LAPW) band structure method.
Abstract: A theoretical approach for the calculation of hyperfine parameters in solids from first principles is presented. These calculations are based on the full potential linearized-augmented-plane-wave (LAPW) band structure method, which is currently one of the most accurate schemes to determine the electronic structure in ordered solids. Exchange and correlation is treated within density functional theory using the generalized gradient approximation. Once the electron density is calculated self-consistently with high accuracy, quantities like electric field gradients (EFG), isomer shifts or hyperfine fields can easily be obtained from this density without further approximations. Using this approach we have studied various systems including metals, insulators, ionic compounds or the highT
c superconductors. In general we find good agreement between theory and experiment, which proves that our method is very accurate. Having these results in mind we are confident that this method is accurate enough to determine the value of the nuclear quadrupole momentQ, provided experimental measurements of the quadrupole coupling constant are available. This procedure is demonstrated forQ of77Se and100Rh, two nuclei recently used in PAC measurements. An extensive study of EFGs at Fe sites in various Fe-compounds has been performed leading to a very reliable quadrupole moment ofQ(57Fe)=0.16 b, a value twice as large as that deduced from recent HF calculations but back to older estimates.
TL;DR: It is shown that spontaneous transition probabilities can be calculated correctly within the framework of the classical approach, and the quadrupole transition probability is shown to be capable of increasing by several orders of magnitude in the neighborhood of the microsphere, to become comparable with the intensity of dipole transitions.
Abstract: The process of quadrupole radiation of an atom in the vicinity of a dielectric sphere is considered within the framework of both quantum-mechanical and classical approaches. It is shown that spontaneous transition probabilities can be calculated correctly within the framework of the classical approach. The quadrupole transition probability is shown to be capable of increasing by several orders of magnitude in the neighborhood of the microsphere, to become comparable with the intensity of dipole transitions, the frequency shifts calculated in the classical approximation being much greater than in the case of dipole transitions. \textcopyright{} 1996 The American Physical Society.
TL;DR: In this paper, a dc superconducting quantum interference device (SQUID) was used to detect 27Al NQR signals in ruby (Al2O3[Cr3+]) at 359 and 714 kHz.
Abstract: A spectrometer based on a dc superconducting quantum interference device (SQUID) has been developed for the direct detection of nuclear magnetic resonance (NMR) or nuclear quadrupole resonance (NQR) at frequencies up to 5 MHz. The sample is coupled to the input coil of the niobium‐based SQUID via a nonresonant superconducting circuit. The flux locked loop involves the direct offset integration technique with additional positive feedback in which the output of the SQUID is coupled directly to a low‐noise preamplifier. Precession of the nuclear quadrupole spins is induced by a magnetic field pulse with the feedback circuit disabled; subsequently, flux locked operation is restored and the SQUID amplifies the signal produced by the nuclear free induction signal. The spectrometer has been used to detect 27Al NQR signals in ruby (Al2O3[Cr3+]) at 359 and 714 kHz.
Patent•
03 Apr 1996TL;DR: A quadrupole mass spectrometer as discussed by the authors comprises an ion source (20), a mass filter (22) and an ion collector (24), the ion source comprises an array (30) of quantum wires.
Abstract: A quadrupole mass spectrometer comprises an ion source (20), a mass filter (22) and an ion collector (24). The ion source comprises an array (30) of quantum wires. The mass filter comprises four glass fibres (32) coated with nickel and the ion collector is an a electrode connected to an integrated complementary metal oxide semiconductor temperature compensated integrated amplifier.
TL;DR: In this article, an elementary method for calculating the interaction energies for a pair of molecules with electric multipole polarizabilities of arbitrary order is presented, where the interaction energy is viewed as arising from two-photon exchange and calculated using fourth order perturbation theory.
Abstract: An elementary method for calculating retarded interaction energies for a pair of molecules with electric multipole polarizabilities of arbitrary order is presented In the multipolar framework of quantum electrodynamics, the interaction energy is viewed as arising from two‐photon exchange and calculated using fourth order perturbation theory It is shown how the energy may be expressed in terms of derivatives of the Casimir–Polder formula written in a special form as an integral over imaginary frequency Explicit formulas are presented for (a) an electric dipole polarizable molecule interacting with an electric quadrupole polarizable molecule, (b) an electric dipole polarizable molecule interacting with an electric octupole polarizable molecule, and (c) an electric quadrupole polarizable molecule interacting with another electric quadrupole polarizable molecule The results are expressed in terms of reducible and irreducible components of multipole moments For case (b) it is shown that in addition to the