Showing papers on "Quadrupole published in 1983"

Excitation phenomena and line intensities in high-resolution NMR powder spectra of half-integer quadrupolar nuclei

Abstract: A theoretical analysis of the general excitation phenomena of half-integer $Ig\frac{1}{2}$ nuclear spins in a strong radio-frequency field shows that coherence between the affected spin states leads to complicated time behavior of the total nuclear magnetization. Very short excitation pulses lead to quantitatively useful high-resolution NMR spectra of quadrupolar nuclei in powder samples spun at the magic angle, while selective spin-state time development during longer rf pulses permits the use of two-dimensional Fourier-transform NMR techniques with simultaneous measurement of the isotropic chemical shifts and the corresponding quadrupole interaction parameters.

The evaluation of hyperfine field distributions in overlapping and asymmetric Mossbauer spectra: a study of the amorphous alloy Pd77.5-xCu6Si16.5Fex

Abstract: It is shown that the presence of asymmetric Mossbauer spectra the distribution of the hyperfine field can be evaluated The calculation of Billiard and Chamberod (1975) is extended to cover spin glasses and metallic glasses, and the results are applied to the series Pd775-xCu6Si165Fex Coupling of the hyperfine field to both the isomer shift and the quadrupole effect is discussed The results can be used to study short-range order changes in alloy glasses

The rotational spectrum and molecular structure of the benzene–hydrogen chloride complex

Abstract: The microwave spectrum of the weakly bound complex benzene–HCl was studied in the gas phase using Fourier transform microwave spectroscopy carried out in a Fabry–Perot cavity with a pulsed supersonic nozzle as the molecular source. Several R‐branch a‐dipole transitions have been observed for benzene–H 35Cl, benzene–D 35Cl, benzene–H 37Cl, and benzene(d6)–H 35Cl. The spectrum was characteristic of a symmetric top, indicating that the time averaged displacement of the H and Cl atoms from the benzene C6 axis is zero. Deuterium substitution of HCl demonstrated that the acidic proton lies between the Cl atom and the benzene ring. The chlorine nuclear quadrupole coupling constant χClaa, was measured for all four isotopic species and is interpreted in terms of a projection of the chlorine quadrupole coupling constant in free HCl, averaged over two degenerate vibrational ground state bending modes involving the angles between the benzene C6 axis and the HCl bond axis. The spectroscopic constants for benzene–HCl are: aNumbers in parentheses represent one standard deviation in the fit.

Electric field-gradient-induced birefringence in N2, C2H6, C3H6, Cl2, N2O and CH3F

Abstract: The optical birefringence induced by an electric field-gradient has been measured in the four non-polar gases nitrogen, ethane, cyclopropane and chlorine, and in the two polar gases nitrous oxide and methyl fluoride Together with known values of the anisotropy in molecular polarizability, the measurements on the non-polar molecules yield the electric quadrupole moments Θ = -4·90 ± 0·3 × 10-40 C m2 for nitrogen, -3·34 ± 0·13 × 10-40 C m2 for ethane, 5·3 ± 0·7 × 10-40 C m2 for cyclopropane and 10·79 ± 0·54 × 10-40 C m2 for chlorine In polar molecules the measured birefringence arises not only from the quadrupole moment, but also from the higher polarizabilities describing the electric dipole induced by an electric field-gradient and a time-varying magnetic field This additional contribution is shown to be small in the case of nitrous oxide, but in methyl fluoride it predominates

Hyperfine interactions of radioactive nuclei

Abstract: 1. Introduction.- 1.1 Perturbed Angular Distribution Techniques.- 1.1.1 Magnetic Hyperfine Interaction.- 1.1.2 Electric Quadrupole Hyperfine Interaction.- 1.1.3 The Stroboscopic Method.- 1.2 Perturbed Angular Correlation Techniques.- 1.3 Nuclear Magnetic Resonance on ?-Emitting Nuclei.- References.- 2. Hyperfine Interactions of Excited Nuclei in Atomic Systems.- 2.1 Free Atoms in Flight-The Recoil Distance Method.- 2.1.1 Calculation of the Perturbation Function GKK(t).- 2.1.2 Fine-Structure Beats.- 2.1.3 Hyperfine Interactions in Free Atoms.- 2.1.4 Hydrogenlike Atoms.- 2.1.5 He-Like Atoms.- 2.1.6 Li-Like Atoms.- 2.1.7 Na-Like Atoms.- 2.1.8 Other Atomic Systems in Vacuum.- 2.2 Atoms in Gases.- 2.2.1 Fast Atoms in Gases.- 2.2.2 Statistical Approach.- 2.2.3 Nuclear Spin Dependence.- 2.2.4 Relaxing the Condition 1/2?C "1.- 2.2.5 The Approach to Thermal Equilibrium-Chemical Effects.- 2.2.6 Thermalized Atoms in Rare-Gas Hosts.- 2.2.7 Pressure Dependence of the Alignment.- 2.2.8 Magnetic Field Dependence.- 2.3 Magnetic Decoupling Measurements in Vacuum.- 2.3.1 Fields Parallel to the Quantization (Beam) Axis.- 2.3.2 Strong Magnetic Fields Transverse to the Beam Direction.- 2.4 New Methods and Future Directions.- References.- 3. Hyperfine Interaction Studies in Nuclear Physics.- 3.1 Overview.- 3.2 Hyperfine Hamiltonian and Nuclear Moments.- 3.2.1 Atomic Isotope Shifts and Nuclear Mean-Square Radii.- 3.2.2 Quadrupole Interactions and Nuclear Quadrupole Moments.- a) Quadrupole Interactions in Atoms.- b) Quadrupole Interaction Non-Cubic Lattices.- c) Calibration of Electric Field Gradients.- 3.2.3 Magnetic Interactions and Nuclear Magnetic Moments.- a) Magnetic Interactions in Atoms.- b) Magnetic Interactions in Solids.- 3.3 Laser Spectroscopy and Hyperfine Structure of Exotic Nuclear States.- 3.4 Nuclear Moments of High-Spin States.- 3.4.1 The Deformation of High-Spin Yrast Isomers.- 3.4.2 The g Factors of Collective High-Spin States.- 3.5 Magnetic Moments of Simple Shell-Model Configurations.- 3.5.1 Meson Exchange Currents.- 3.5.2 First-Order Core Polarization.- 3.5.3 High-Spin Isomers of Two-Particle Configuration.- 3.5.4 Single-Particle States in Other Mass Regions.- 3.5.5 Core-Polarization Blocking.- 3.5.6 Second-Order Core Polarization.- 3.5.7 Magnetic Moments of ? Emitters.- 3.6 Hyperfine Interactions in Nuclear ? Decay.- 3.6.1 Theoretical Position.- 3.6.2 Experimental NMR Techniques for ? Emitters.- 3.6.3 Experimental Results.- 3.6.4 Discussion.- References.- 4. Hyperfine Interactions of Defects in Metals.- 4.1 Relevant Solid State and Nuclear Physics Aspects.- 4.1.1 Defects in Metals.- a) Defects After Irradiation.- b) Defects in Thermal Equilibrium.- c) Vacancy and Interstitial Configurations.- d) Migration of Defects.- e) Interaction of Lattice Defects with Impurity Atoms.- f) Some Experimental Aspects in the Determination of Defect Properties.- 4.1.2 Hyperfine Interaction Parameters.- a) Electric Hyperfine Interaction.- b) Magnetic and Combined Hyperfine Interaction.- 4.1.3 Nuclear Probes.- 4.2 Hyperfine Investigations of Defects.- 4.2.1 Experiments with Radioactive Sources.- a) Diamagnetic fcc Metals.- b) Diamagnetic bcc Metals.- c) Ferromagnetic Cubic Metals.- d) Hcp Metals.- e) Summary.- 4.2.2 In-Beam Experiments.- a) Cubic Metals.- b) Noncubic Metals.- c) Summary of Nuclear Reaction Experiments.- References.- 5. Electric Quadrupole Interaction in Noncubic Metals.- 5.1 Electric Quadrupole Hyperfine Interaction.- 5.2 Experimental Methods.- 5.2.1 Energy Methods.- a) Specific Heat Measurements.- b) Nuclear Orientation.- c) Mossbauer Effect.- 5.2.2 Precession Methods.- a) Nuclear Resonance Methods.- b) Perturbed Angular Correlation (Distribution) Methods.- 5.3 Experimental Data and Systematic Trends.- 5.3.1 The Universal Correlation.- 5.3.2 The Temperature Dependence of the EFG.- 5.3.3 The Pressure Dependence of the EFG.- 5.3.4 Impurity Valence Effects of the EFG.- 5.4 The EFG in Metals.- 5.4.1 Anti shielding.- 5.4.2 The Lattice Sum.- 5.4.3 Wave Function Approaches.- a) Wannier Functions.- b) Augmented Plane Waves.- c) Orthogonalized Plane Waves.- d) Fermi Surface Electrons.- 5.4.4 Potential Approaches.- 5.4.5 Temperature Dependence.- a) Fermi Surface Electrons.- b) Wave Function Approach.- c) Potential Approach.- 5.4.6 Pressure and Concentration Dependence.- 5.5 Conclusion.- 5.6 Appendix.- Table of Experimental Data on Quadrupole Interaction in Noncubic Metals.- References.- 6. ? Emitters and Isomeric Nuclei as Probes in Condensed Matter.- 6.1 Theory.- 6.1.1 Hamiltonian and Energy Levels.- 6.1.2 Reorientation in Electromagnetic Fields.- 6.1.3 Relaxation.- a) Nuclear Relaxation by Magnetic Coupling to Conduction Electrons.- b) Relaxation by Fluctuating Nuclear Dipole-Dipole Interactions.- c) Quadrupolar Relaxation Induced by Atomic Motion.- d) Relaxation by Quadrupolar Spin-Phonon Coupling.- 6.2 Experimental Methods.- 6.2.1 Experiments Using ? Emitters.- a) Probe Creation by Capture of Polarized Thermal Neutrons.- b) Probe Creation by Fast Particle Reactions with Selected Recoil Angle.- c) Probe Creaction by Reactions with Polarized Fast Particles.- d) Probe Creation by Fast Particle Reactions and Subsequent Polarization in the Stopper.- 6.2.2 Experiments Using Isomeric ? Emitters.- 6.3 Metals.- 6.3.1 Static Interactions, NMR Spectra.- a) Magnetic Energy Splitting.- b) Energy Splitting in the Presence of Quadrupole Interactions.- 6.3.2 Relaxation of Nuclear Orientation.- a) Solid Metals.- b) Liquid Metals.- 6.4 Insulators.- 6.4.1 Static Interactions, NMR Spectra.- a) Lithium Compounds.- b) Fluorine Compounds.- c) Probe Nuclides in the Mass Number Range 24 ? A ? 39.- d) Indium and Silver Compounds.- 6.4.2 Relaxation of Nuclear Orientation.- a) Lithium and Fluorine Compounds.- b) Indium and Silver Compounds.- 6.5 Tabular Summary.- References.

Electric field gradients in metals

Abstract: Data published up to June 1986 have been taken into account. All experimental values are expressed in terms of the quadrupole interaction frequency as defined by eq. (1). The entries are listed order of increasing atomic and mass number of the probe. Energy, spin, half-life and where available the quadrupole moment of the level are given for each probe. Where no reference is given the values for the quadrupole moments have been taken from ref. [310]. The columns of the table contain the following quantities:

Potential pockets in the 238 U+ 238 U system and their possible consequences

Abstract: Within the double-folding model the separation, shape, and orientation dependence of the interaction potential is studied for two heavy ions. An effective nucleon-nucleon interaction (M3Y) derived fromG-matrix elements and based upon the Reid soft-core potential is used. Deformed Fermi-type matter densities with static quadrupole and hexadecapole deformations were utilized. The model is applied to the238U+238U system and shows dramatic dependence on the deformations and orientations.

Quadrupole Stabilization of the n = 2 Rotational Instability of a Field-Reversed Theta-Pinch Plasma

Abstract: The n = 2 rotational instability is the most dangerous gross instability in a field-reversed theta pinch. It is demonstrated for the first time that the instability is completely suppressed by superposing a quadrupole field which is much smaller than the axial confinement field at the separatrix. The experimental threshold intensity of the field for stabilization is about 2.5 times less than that predicted by theoretical stability analysis.

3-mm Anisotropy Measurement and the Quadrupole Component in the Cosmic Background Radiation

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

Multipole N.M.R.: IV. Dynamics of single spins

Abstract: Using a multipole operator basis general formulae are obtained which describe the time evolution of the complete density matrix for a spin of arbitrary magnitude interacting with an electric field gradient in a static magnetic field and subject to a sequence of pure (δ-function) pulses. The evolution under the quadrupole interaction is calculated from general non-equilibrium conditions for I ⩽ 9/2. The physical significance of the results and descriptions of the multiquantum spectra are given along with some results of some two-pulse sequences.

High-resolution measurements of isotope shifts and hyperfine structure in stable and radioactive lead isotopes

Abstract: The authors present new measurements of isotopic shifts and hyperfine structure in the lead resonance line for a total of 15 isotopes. The experimental accuracy is of order 4 MHz. Using independent measurements of the nuclear parameter lambda for the stable isotopes they have derived lambda for all measured isotopes. The derived values of lambda are compared with various theoretical predictions for the lead nuclei. The authors also give values for the nuclear magnetic dipole and electric quadrupole moments deduced from the measurements.

The structure and molecular properties of the acetylene–HCN complex as determined from the rotational spectra

Abstract: The microwave spectra for four isotopic species of a complex formed between acetylene and HCN have been obtained using the pulsed, Fourier‐transform method with gas pulsed into an evacuated Fabry–Perot cavity. The spectra indicate the complex to be a T‐shaped near‐prolate asymmetric rotor (κ=−0.993) in its ground vibrational state in which HCN lies on the C2 symmetry axis with the hydrogen atom of HCN pointing to the middle of the triple bond of acetylene. The carbon atom of HCN is situated 3.656 A from the acetylene center of mass. Nuclear quadrupole coupling constants for N are obtained for all four isotopes and deuterium quadrupole coupling constants are obtained for two isotopes. Various contributions to the electric field gradients at quadrupolar nuclei are discussed.

The microwave spectrum and molecular structure of N2–HCl

Abstract: The structure of the van der Waals molecule N2–HCl has been determined by molecular beam electric resonance spectroscopy. The microwave spectrum is well fitted by a linear hydrogen‐bonded structure with the following spectroscopic constants: Constant 14N2–H 35Cl 15,14N2–H35Cl 14,15N2–H35Cl In addition, spectra for the two chlorine isotopes of the complex formed using 15N2 are presented and analyzed. Electric quadrupole coupling hyperfine structure of 14N and 35,37Cl, is used to determine the vibrationally averaged orientation of the submolecules. The HCl submolecule makes an average angle of 26° with the a axis of the complex in all isotopes studied, while the average angle for the N2 submolecule is estimated to be 19°. The hydrogen–bond length is 2.42 A in the linear configuration which is virtually identical to the hydrogen‐bond length in OC–HCl. It is shown that the electric dipole moments of a series of N2 and CO complexes are not simply related to the polarizabilities of N2 and CO. Analysis of the induced difference in the quadrupole coupling constants of the two nitrogen nuclei indicates a transfer of 0.036 of an electron from the outer to the inner nitrogen which will affect the observed dipole moment.

The translational-rotational absorption spectrum of hydrogen

Abstract: The collision-induced translational–rotational spectrum of H2 has been accurately measured in the region from about 30 to 2000 cm−1 at 195 and 297 K. A very weak feature due to the hexadecapole-induced dipole, the U0(1) line, has been detected at 195 K in the region around 1622 cm−1. These spectra can be accurately represented by a simple, semi-empirical line shape. The effect of double transitions are considered and explicit expressions for these are given. Spectral integrals proportional to the zero and first moments are determined experimentally and compared with the theoretical moments computed on the basis of quadrupole induction for several potentials. The difference between the experimental and theoretical values, in the order of 20%, is attributed to anisotropic overlap induction, but the inferred magnitude of this component is strongly dependent on the assumed potential.

Determination of the 14N quadrupole coupling tensors and the 13C chemical shielding tensors in a single crystal of L‐asparagine monohydrate

Abstract: The 14N quadrupole coupling tensor for the NH3+ nitrogen nucleus in a single crystal of l‐serine monohydrate was completely determined. The quadrupole coupling constant, and the asymmetry parameter, were evaluated to be e2Qq/h=1.069 MHz and η=0.214 at room temperature by measuring the angular variation of the proton‐enhanced 14N NMR spectra about the three experimental axes. It was found that the direction of the largest principal value of the 14N quadrupole coupling tensor is at an angle of 3.5° to the direction of the C–N bond. The sign of the 14N quadrupole coupling constant was determined to be positive by analyzing the 13C–14N dipolar splitting pattern in the 13C NMR signal of the Cα carbon. The 13C chemical shielding tensors for three chemically different carbon nuclei, namely COO−, Cα, and Cβ were determined and assigned to the molecule in the unit cell by inspecting the 13C–14N dipolar interaction rather than relying only on the local symmetry. The most shielded direction of the COO− carbon is per...

Determinations of structure and bonding in amorphous SiO2 using 17O NMR

Abstract: Isotopically enriched SiO 2 was fabricated by hydrolysis of SiCl 4 with H 2 O enriched to 50% in 17 O. The presence of hydrogen in the resulting powder was investigated using 1 H NMR. The study revealed that the hydrogen was present in superficial hydroxyl groups, which could be removed by outgassing at 500°C. Well-defined structure in the SiO 2 17 O spectrum arises from quadrupole effects and indicates significant local order in the material. A computer simulation of the spectrum was obtained assuming a Gaussian distribution of the quadrupole coupling constant ( Q cc ) and the asymmetry parameter (η) for the oxygen site. The most probable values of the coupling constant ( Q cc 0 5.17 MHz) and the asymmetry parameter ( η 0 = 0.2), and their standard deviations ( σ Q cc = 0.7 MHz, σ η = 0.2) were obtained from the simulation. These quadrupole parameters and their Gaussian widths were used in a Townes-Dailey calculation, which relates the quadrupole parameters to the charge density in the oxygen electronic orbitals. This calculation is consistent with the SiOSi bond angle (α) having a distribution of values (130° ⩽ α ⩽ 180 °), and it weakly supports the presence of π bonding between the silicon 3d and oxygen 2p orbitals.

The microwave spectrum of the SiN(2Σ+) radical

Abstract: The microwave absorption spectrum of the SiN radical has been detected in a dc glow discharge in a SiCl4 or SiH4/N2 mixture. The three rotational transitions N=2←1, 3←2, and 4←3, have been observed in the frequency region 87 to 175 GHz by using a source‐frequency modulation microwave spectrometer. The rotational constant, the centrifugal distortion constant, the spin‐rotation coupling constant, and the magnetic hyperfine coupling constants b and c and the electric quadrupole coupling constant of the nitrogen nucleus have been precisely determined. The electronic structure of the SiN molecule has been briefly discussed using the magnetic hyperfine coupling constants and also the quadrupole coupling constant [3.05(23) MHz] of 14N.

83Kr nuclear quadrupole coupling, microwave spectrum, and structure of KrHCN

Abstract: Rotational spectra have been observed for ten isotopic species of KrHCN using the pulsed Fabry–Perot Fourier transform technique. The 83Kr nuclear quadrupole coupling constant has been measured in 83KrHC 14N, 83KrHC 15N, and 83KrDC 14N. Values of the rotational constants B0, centrifugal distortion constants DJ and H, 14N and 83Kr nuclear quadrupole coupling constants are These constants are consistent with a linear or near‐linear configuration, with a Kr–HCN center‐of‐mass separation of 4.54 A, and the Kr atom located 27° off the HCN figure axis on average, where the vertex of this angle is placed on the HCN center‐of‐mass. KrHCN exhibits unusually large centrifugal distortion in comparison to previously studied Kr–hydrogen halide systems. We find that the measured 83Kr nuclear quadrupole coupling constants in 83KrHC 14N and 83KrDC 14N are consistent with a long range polarization model previously used to explain values of χKr in KrH(D)Cl and KrH(D)F.

Finite-field many-body perturbation theory

Abstract: The results of complete fourth order many-body perturbation theory (MBPT) calculations of the quadrupole moment tensor for the FH and H2O molecules are presented. The finite-field method employed in this study is based on the coupled Hartree-Fock (CHF) solutions for the externally perturbed system. The results are very close to the available experimental data. Of interesting features of the correlation perturbation series for the quadrupole moment components one should mention that the fourth order correlation correction is dominated by contributions involving triple and single substitutions in the reference Hartree-Fock function. Moreover, the correlation perturbation series for quadrupole moments appears to be less regular than the corresponding series for molecular dipole moments. Additionally complete fourth order MBPT calculations are performed for the quadrupole polarizability tensor of FH and H2O. The correlation corrections to the corresponding CHF values are large and exhibit similar regularities...