Showing papers on "Quadrupole published in 1982"

Molecular and structural information from 14N–13C dipolar couplings manifested in high resolution 13C NMR spectra of solids

Abstract: The dipolar coupling between 14N and 13C is not suppressed by magic angle sample spinning because the relatively large 14N quadrupole interaction shifts the axis of quantization of the 14N spins away from the direction of the applied field. The resulting 13C resonance line shapes are influenced by the sign, magnitude, and asymmetry parameter of the 14N quadrupole coupling tensor; the internuclear distance; the magnitude of the applied magnetic field; and the orientation of the internuclear vector in the principal axis system of the electric field gradient. It is demonstrated that one or more of these parameters can be determined from the 13C NMR data if the others are known by virtue of single crystal studies or molecular symmetry.

Electric field gradients and charge density in corundum, α-Al2O3

Abstract: The charge density in α-Al2O3 has been refined with respect to X-ray structure factors [complete spheres for both Mo Kα and Ag Kα radiations with (sin θ/λ)max = 1.19 and 1.495 A-1 respectively] and electric-field gradient tensors at both atomic sites, using Hirshfeld- type deformation functions. Atomic charges from a κ refinement are + 1.32 (5) for Al and -0.88 (8) e for O. The charge distribution of O is polarized towards the four Al neighbours, and metal-metal bonds are clearly absent. Quadrupole coupling constants and asymmetry parameters of the field-gradient tensors cannot be determined from the structure factors. They define the quadrupolar deformations near the atomic centers, and the X-ray data define the charge density between the atoms. The orientational parameters of the tensors and the signs of their largest eigenvalues can be qualitatively retrieved from the X-ray data. The refinement of anisotropic secondary-extinction parameters may, however, destroy this information. Refinement with respect to the field gradients affects mainly the quadrupolar deformation terms, and has little influence on the X-ray scale factor (i.e. monopolar terms) and computed electrostatic fields (i.e. dipolar terms). Properties of the charge density with different angular symmetries are thus only weakly correlated.

Variable‐angle sample‐spinning high resolution NMR of solids

Abstract: We have obtained high‐resolution solid‐state NMR spectra of a variety of nonintegral‐spin quadrupolar nuclei (23Na, 51V, and 55Mn) under conditions of ‘‘magic‐angle’’ sample‐spinning (MASS) and ‘‘variable‐angle’’ sample‐spinning (VASS). We show for systems in which the second‐order quadrupole interaction dominates the breadth of the (1/2,−1/2) spin transition, that optimum line narrowing is achieved by rapid sample rotation at angles other than the familiar θ=54.7° ‘‘magic‐angle.’’ The effect originates in the more complex angle dependence of the second‐order quadrupole interaction, rather than the more familiar P2 (cos θ) dependence of dipolar and chemical shift interactions, and theoretical VASS line shapes for a variety of spinning angles, and electric field gradient tensor asymmetry parameters (η), are presented. We show that VASS NMR at low fields generates complex spectral line shapes, which at some angles exhibit well‐resolved centerbands and spinning sidebands. We also discuss briefly, with exampl...

Rotational excitation of N2, CO and H2O by low-energy electron collisions

Abstract: Absolute total and differential rotational and rotational-vibrational cross sections have been measured for N2 (weak quadrupole), CO (weak dipole), and H2O (strong dipole). In the beam experiments, the range of collision energies of the electrons was chosen between 0.5 and 6 eV, and the range of scattering angles from 15 to 105 degrees was covered. The overall energy inhomogeneity of the electron spectrometer was between 10 and 18 meV FWHM, depending on the experiment. Direct and resonant rotational excitation has been measured. In the case of N2 the rotational branches with Delta J=0, +or-2, +or-4 have been fitted to energy-loss spectra and for each branch a cross section is given. The authors have proceeded similarly in the case of CO (for dipole excitation Delta J=0, +or-1, for excitation via the 2 Pi resonance Delta J=0, +or-1, ..., +or-4) and in the case of H2O ( Delta J=0, +or-1). For N2 and CO the results are compared with calculated angular dependences. Finally, the cross sections are listed according to the different types of interaction potentials and interaction mechanisms.

The use of triple quadrupoles for sequential mass spectrometry: 1—The instrument parameters

Abstract: Triple quadrupoles are becoming widely used in sequential mass spectrometry. The observed spectra are very dependent upon the choice of instrument parameters such as the gas target density, the mode of operation of the central quadrupole, and the direct current levels of the quadrupoles (rod-offsets) which determine the collision energy and the maximum mass resolutions in each analysing quadrupole. The influence of each of the instrument parameters is discussed with examples of experimental measurements of performance, and the optimum choice of modes of operation is determined.

The role of microwave frequency in epr spectroscopy of copper complexes

Abstract: In this paper we review all experimental approaches to the analysis of electron paramagnetic resonance (EPR) spectra of Cu2+ where either the choice of microwave frequency or variation of microwave frequency are crucial elements of the methodology. We do not restrict ourselves to copper proteins, but it is our hope that, by considering the literature from this perspective, useful insights can be obtained into optimization of the design of future experiments on proteins. Three major areas where microwave frequency is crucial have been defined. 1. State mixing, both electronic and nuclear, depends on the magnitude of the applied magnetic field relative to other interactions. Nuclear state mixing depends on the relative magnitudes of the nuclear Zeeman, nuclear hyperfine, and nuclear quadrupole interactions. When they be­ come comparable, mixing occurs, or classically the axis of quantization (around which precession occurs) is no longer coincident with the applied field. Forbidden transitions involving change in nuclear quantum number occur, and they can be of considerable interest, particularly in determina­ tion of quadrupole couplings.

Second-order contributions to gravitational deflection of light in the parametrized post-Newtonian formalism

Abstract: By considering the largest of the post-post-Newtonian terms, we have developed a parametrized expansion of the solar metric to one order beyond the linear terms. Using this parametrized post-linear metric we calculate the orbits of photons in the Sun's equatorial plane and the resulting deflection. The results depend on four of the usual parametrized post-Newtonian parameters and five new parameters, as well as on the Sun's total angular momentum and quadrupole moment parameter. Jovian light deflection is also examined.

Spin lattice relaxation of dipole nuclei (I = 1/2) coupled to quadrupole nuclei (S = 1)

Abstract: Nuclear magnetic relaxation has been investigated for dipole nuclei (I = 1/2) coupled to quadrupole nuclei (S = 1) by dipolar interaction. Quadrupole dips in the frequency dependence of the longitudinal relaxation time of the I-spins are predicted under certain conditions. Relaxation dispersion experiments have been performed with Bovine Serum Albumin, which contains 14N1H-groups as representatives of the envisaged class of two-spin systems. In the dry and hydrated protein, quadrupole dips have been observed. The conclusion is that near room temperature and up to frequencies of the order of at least 107 Hz the 14H1H-groups are the dominant relaxation centres. The relevance for investigations of other biological systems is briefly discussed.

3 mm Anisotropy Measurement: On the Quadrupole Component in theCosmic Background Radiation

Abstract: We have mapped the large-scale anisotropy in the cosmic background radiation at 3 mm wavelength using a liquid-helium-cooled balloon-borne radiometer sensitive enough to detect the dipole in one gondola rotation (1 minute). Statistical errors on the dipole and quadrupole components are below 0.1 mK with less than 0.1 m K galactic contribution. We find a dipole consistent with previous measurements but disagree with recent quadrupole reports. The measurement is also useful in searching for spectral distortions.

The multipole-extracted adiabatic-nuclei approximation for electron-molecule collisions

Abstract: An extension of the adiabatic-nuclei approximation appropriate for electron collisions with polar molecules is discussed. The method will find a most useful application, but is not restricted, to molecules with large permanent dipole moments. Treatment of molecules with small or negligible dipole moments but significant quadrupole moments and/or dipole polarizabilities is also within its purview. The essence of the method consists of extracting the effects of the long-range interactions from the usual adiabatic-nuclei expressions, and reintroducing them in the laboratory frame in a self-consistent manner. The first Born approximation is the simplest, but not the only possible, vehicle for this approach. The method is closely related to the angular-frame transportation method. Illustrative applications are presented.

Review paper: Design of a mass and ion kinetic energy spectrometer for organic chemical work

Abstract: The design of a mass spectrometer for the determination of the structural formulae of organic compounds is discussed. The ion-optical characteristics of electric and magnetic sectors and also of quadrupole mass analysers are considered and the additional information that can be gleaned when such components are combined in various ways is listed. The advantages of using collision cells for inducing fragmentation of selected ion species are listed including those that result when the collision cell is floated at an electrical potential different from that of the incident ion beam. Important performance characteristics are the resolution with which a particular ion may be selected and the resolution with which daughter ions formed from it can be separated. It is concluded, that for instruments comprising three analysing units together with the appropriate collision cells, the most versatile combinations and those with the highest performance are an arrangement consisting of a magnetic sector followed by an electric sector, this being followed either by a further magnetic sector or a quadrupole. The properties of these two systems are compared in detail.

Linearized quadrupole waves in general relativity and the motion of test particles

Abstract: We write out the explicit form of the metric for a linearized quadrupole gravitational wave in the transverse-traceless gauge. We give a collection of formulas which are useful for testing numerical codes to integrate the full nonlinear Einstein equations. We also show that a test particle initially at rest acquires no energy from a linearized gravitational wave.

Preliminary determination of the sun's gravitational quadrupole moment from rotational splitting of global oscillations and its relevance to tests of general relativity

Abstract: The sun's internal angular velocity is estimated from observations of rotational splitting of low-order, low-degree global oscillations detected as fluctuations in the limb-darkening function. The inferred rapid rotation implies a unitless gravitational quadrupole moment, J/sub 2/, of (5.5 +- 1.3) x 10/sup -6/. When this result is combined with two published planetary radar results values of 0.987 +- 0.006 and 0.991 +- 0.006 are obtained for (1/3)(2+2..gamma..-..beta..), a quantity equal to one in the general theory of relativity. .ID LRK206 .PG 1798 1798

Fourier Transform Nuclear Quadrupole Resonance Spectroscopy

Abstract: FT-NQR (Fourier Transform Nuclear Quadrupole Resonance) spectroscopy is one of the newer analytical tools. Although nuclear quadrupole coupling constants were first observed in atoms by Schmidt and Schuler1 in 1935 and in molecules by Kellog2 and coworkers in 1936, it was the discovery of pure quadrupole coupling transitions in solids by Dehmelt and Kruger3,4 in 1950 and 1951 that initiated the understanding of the NQR phenomenon as presently utilized.

Electric quadrupole moments and isotope shifts of radioactive sodium isotopes

Abstract: On-line high resolution laser spectroscopy has been performed on radioactive /sup 20 -31/Na. New values for the isotope shift of the D/sub 1/ line of /sup 20-24,31/Na relative to /sup 23/Na have been obtained. The spectroscopic quadrupole moments of /sup 21,25-29/Na have been determined using a double resonance method. The D/sub 2/ line hyperfine structure of /sup 21,25-27/Na has also been studied by laser optical spectroscopy. Results are in agreement with those obtained by rf double resonance. No evidence of the sudden onset of a deformation expected at N = 20 has been found. A strong shell effect in the change in the mean-square charge radius is exhibited at N = 14.

Internal rotation and gravitational quadrupole moment of the Sun

Abstract: The internal angular velocity of the Sun is estimated from observations of apparent rotational splitting of low-order low-degree global oscillations detected in fluctuations in the limb-darkening function. A sidereal rotation of 3 µHz is inferred for the deep interior; this is more than six times greater than the equatorial rotation frequency of the photosphere. The inferred angular velocity distribution does not vary strongly with latitude, and yields a gravitational quadrupole moment J2≃3.6×10−6. When combined with the results of planetary radar observations to determine (2−β+2γ)/3, a combination of Eddington–Robertson post-newtonian parameters which in general relativity is unity, a value of about 0.994 (±0.012) is thus obtained.

The structure and hyperfine constants of HF–Cl2

Abstract: Molecular beam electric resonance studies on two isotopes of HF–Cl2 have enabled the following spectroscopic constants to be determined: These constants are best interpreted in terms of an equilibrium structure for HF–Cl2 in which the three heavy atoms form a linear array with an F–Cl bond length of 2.96 A. The proton is off‐axis with an H–F–Cl angle of 125°. The chlorine quadrupole coupling constants show a charge distortion of the chlorine submolecule. Precise interpretation of eQq is hindered by lack of a value for the coupling constant of free 35Cl2.

An achromatic quadrupole lens doublet for positive ions

Abstract: The resolution and chromatic aberration of a doublet of achromatic quadrupole lenses have been experimentally measured. Each achromatic lens is of length 5.99 cm and comprises an electric quadrupole of bore 1.05 mm and a magnetic quadrupole of bore 3.40 mm. In preliminary tests with 600‐keV protons, a chromatic aberration coefficient of less than 1.2 cm and beam width of 4 μ are measured, compared to 20 cm and 4 μ for the same doublet operated in a solely magnetic mode.

Precision measurement of the electric quadrupole interaction in zinc metal

Abstract: To decide on the validity of various values for the quadrupole coupling constant of Zn metal available in the literature, we have used the frequency modulation technique to the 93.3 keV Mossbauer resonance of67Zn. We obtained for a67Zn metal absorber: e2qQ/h =vO = 12.34 ± 0.03 MHz. The asymmetry parameter was found to be η=0.00 −0 +0.06 . These precise values can be used as a calibration standard for67Zn Doppler drives.