Showing papers on "Quadrupole published in 1975"

Ligand-polarization contributions to the intensity of hypersensitive trivalent lanthanide transitions

Abstract: The oscillator strengths of the hypersensitive f-electron transitions in lanthanide(III) complexes, the quasi-quadrupolar transitions with intensities sensitive to the ligand environment, are found to arise principally from the coulombic correlation between transient induced electric dipoles in the ligands and the f-electron quadrupole moments of the metal ion. The correlation gives a non-zero resultant electric dipole transition moment in complexes belonging to the point groups, Dp and Cpv , with p unrestricted, C 3h , D 3h , Td , and their subgroups, the mechanism being forbidden where there is inversion symmetry or an Sp axis with p ⩾ 5. The theory accounts quantitatively for the hypersensitive oscillator strengths of the lanthanide trihalides, which range over two orders of magnitude, and the substituent effects observed in the lanthanide tris-β-dicarbonyl chelate complexes. The restriction of hypersensitivity to the qudrupolar f-electron transitions is discussed.

Excitation and Detection of Coherence between Forbidden Levels in Three-Level Spin System by Multi-Step Processes

Abstract: The coherent superposition of the states between which magnetic dipole transition is forbidden has been excited and detected by means of a multi-step application of resonant rf pulses in a three-level NMR system. The experiment was carried out on 27 Al nuclei in Al 2 O 3 where the quantization axes of the quadrupole and the magnetic coupling were parallel. Free decay and echo signals associated with the coherence were observed, and transfer of coherence between nonresonant pairs of levels was studied in detail.

Calculation of the hyperfine interaction using an effective-operator form of many-body theory

Abstract: The effective-operator form of many-body theory is reviewed and applied to the calculation of the hyperfine structure. Numerical results are given for the $2p$, $3p$, and $4p$ excited states of Li and the $3p$ state of Na. This is the first complete calculation of the hyperfine structure using an effective-operator form of perturbation theory. As in the Brueckner-Goldstone form of many-body theory, the various terms in the perturbation expansion are represented by Feynman diagrams which correspond to basic physical processes. The angular part of the perturbation diagrams are evaluated by taking advantage of the formal analogy between the Feynman diagrams and the angular-momentum diagrams, introduced by Jucys et al. The radial part of the diagrams is calculated by solving one- and two-particle equations for the particular linear combination of excited states that contribute to the Feynman diagrams. In this way all second- and third-order effects are accurately evaluated without explicitly constructing the excited orbitals. For the $2p$ state of Li our results are in agreement with the calculations of Nesbet and of Hameed and Foley. However, our quadrupole calculation disagrees with the work of Das and co-workers. The many-body results for Li and Na are compared with semiempirical methods for evaluating the quadrupole moment from the hyperfine interaction and a new quadrupole moment of $^{23}\mathrm{Na}$ is given.

Pyrolysis of ethylamine. I. Microwave spectrum and molecular constants of vinylamine

Abstract: Microwave rotational spectra assignable to gas phase vinylamine (CH2=CHNH2) have been detected in the pyrolysis decomposition products of ethylamine. Stark effect and hyperfine structure measurements have aided the assignment of the spectrum and allow the determination of the 14N nuclear electric quadrupole coupling constants and the electric dipole moment for vinylamine. The spectrum of the first excited inversion vibrational state has been assigned. Relative intensity measurements indicate that the inversion state lies about 65±25 cm−1 above the ground state. The spectral evidence suggests that vinylamine has a nonplanar equilibrium structure with r0(C−N) = 1.40 A and &CCN = 125°.

Fine and hyperfine structure of the 2 2 P term of 7 Li; determination of the nuclear quadrupole moment

Abstract: Microwave transitions between the Zeeman split doublet states 22 P 1/2 and 22 P 3/2 of7Li have been measured using the optical double resonance method. The fine structure separation was determined to bev fs=10.053.184(58) MHz. The hyperfine structure was well resolved and led to considerably improved precision of the diagonal coupling constantsa 1/2=45.914(25) MHz,a 3/2=−3.055(14) MHz,b=−0.221(29) MHz. Furthermore, the contact, spin dipolar and orbital magnetic hyperfine constants are evaluated using additional results from level crossing experiments, which are more sensitive on the non-diagonal magnetic hyperfine constanta 3/2,1/2. The results are in good agreement with recent theoretical calculations. The nuclear quadrupole moment is derived fromb to beQ(7Li)=−41(6) mbarn.

Crystal dynamics of nitrogen: The cubic α-phase

Abstract: The technique of inelastic neutron scattering has been used to determine translational and librational lattice modes in a single crystal of solid nitrogen in the cubic $\ensuremath{\alpha}$-phase at 15 K. The measurements were concentrated at the high-symmetry points $\ensuremath{\Gamma}$, $R$, and $M$, where the degeneracies ease the task of symmetry assignments to the observed modes. The assignment was made on the correlation of the observed structure-factor variation with force-model predictions. The calculations were based on a general potential function which includes Lennard-Jones or six-exponential-type interactions as well as electric quadrupole forces. Good agreement was found between both the observed frequencies and the observed intensities and their calculated counterparts. The temperature dependence of selected modes has been established and it is compared to a recent self-consistent phonon calculation.

Evidence for the isoscalar giant quadrupole resonance in $sup 16$O

Abstract: The spectra of 146-MeV $\ensuremath{\alpha}$ particles scattered inelastically from $^{16}\mathrm{O}$ exhibit a giant-resonance-type structure between excitation energies of 15.9 and 27.3 MeV. The analysis of angular distributions shows its quadrupole nature and yields a strength exhausting about 65% of the isoscalar $E2$ energy-weighted sum rule.

Multipole moments of the hydrogen molecule

Abstract: For small internuclear distances, the quadrupole moment of the hydrogen molecule is quadratic in the internuclear distance, with a coefficient determined by the quadrupole shielding factor of the h...

Magnetic multipole moments

Abstract: Literature definitions of magnetic multipole moment operators are shown to be at variance, and new definitions are formulated which are consistent with a general multipole interaction hamiltonian and with the radiation field of a dynamic charge distribution. The applicability of traceless multipole moments is examined. The multipole hamiltonian is used to derive expressions for some magnetic quadrupole distortion tensors. For those describing the quadrupole moment induced by a magnetic field and by a field gradient the number of independent components for various molecular symmetries is evaluated.

Etude Expérimentale et Théorique de l'Iode Atomique. Observation du Spectre d'Arc Infrarouge, Classification et Structure Hyperfine

Abstract: The infrared spectrum of 127I, nuclear spin I = 5/2, has been observed between 3 000 and 11 500 cm-1 at high resolution by means of the Fourier transform spectrometry method. We have observed 440 structures. Precise measurements of the centre of gravity of these structures give energy levels with an error less than 0.005 cm-1. We have analysed 130 hyperfine structures, giving the magnetic dipole and the electric quadrupole hyperfine structure constants for 37 even levels and 42 odd levels. The intermediate coupling has been studied for the even configurations 5s25p4(6s + 7s + 5d + 6d) + 5s5p6 simultaneously, and for the odd configurations 5s25p4 (6p + 7p) and 5s25p44f. Using the wavefunctions obtained, hyperfine structure parametric studies have been performed, giving the H.F.S. monoelectronic constants a(nl) and b(nl). An a priori study of hyperfine structure, using the relativistic central potential method makes clear the important contribution of relativistic effects and leads one to think that distant configuration interaction effects are negligible in the excited configurations which have been studied.

Molecular structure, quadrupole splitting, and magnetic susceptibility of iron in deoxygenated myoglobin and hemoglobin

Abstract: For three stereo-structural models of deoxymyoglobin (Mb) and deoxyhemoglobin (Hb) we derive electronic configurations and their mutual spin-orbit coupling. From the temperature dependent molecular electric field gradient (EFG) tensor we calculate temperature dependent quadrupole splittings, ΔE q(T), asymmetry parameters, η(T), and orientations of the EFG component V zz(T) with respect to the heme group. Comparing theoretical and experimental data we find a molecular electronic structure, which then is used to compute temperature dependent magnetic susceptibilities, χ(T). Theoretical and experimental χ(T) data are in reasonable agreement. From the consistency of our model calculations with experimental results we conclude that iron in Mb and Hb probably is pentacoordinated and considerably out of the heme plane by 0.4–0.8 A.

Relaxation Rates of Excited Nuclei in Liquid Metals

Abstract: Perturbed angular distribution methods (PAD) following nuclear reactions were applied to relaxation phenomena of excited nuclear states in liquid Ga, In, InGa alloys, Te, Hg, Tl, and Pb. Due to the selection of excited states with small g-factors the quadrupole relaxation rate τQ-1 in these metals, except in Tl, could be observed as the dominant contribution to the total rate at lower temperatures. It is suggested that the τQ-1 rates in Ga, In, InGa and Hg are essentially due to the diffusion induced mechanism while the interpretation of τQ-1 in Pb and Te is more complicated. Further magnetic relaxation rates of isolated impurities are deduced for four systems and quadrupole moments of ms-states in 71Ge, 115Sn, 205Pb, and 206Pb are derived from the quadrupole relaxation rates.

Calculation of Magnetic and Electric Hyperfine Fields in Metals

Abstract: This article is divided into two parts. The first part deals with the theory of the origin of hyperfine fields in ferromagnetic iron and cobalt, while the second part deals with the theory of nuclear quadrupole interaction in pure non-cubic metals. In the first part, dealing with hyperfine fields in ferromagnets, the various mechanisms that can produce the hyperfine field are reviewed and their contributions, as obtained from calculated band wave-functions are analysed. Comparison is made with experiment and the possible improvements needed in the electric theory are discussed. In the second part of the article, the electronic field-gradients in a number of hcp metals are discussed. The ionic and electron contributions are analysed and comparison is made with experimental data with respect to both magnitude and sign of the quadrupole coupling constants where available. The nature of the accuracy to be expected from the use of wave-functions obtained by actual potentials and pseudo-potentials is discussed. The implications of theoretical results in the pure metals for nuclear quadrupole interaction in alloys is discussed. In the alloys, a substantial amount of experimental data is available currently by the perturbed angular correlation and other techniques.

Observation of a pure electric quadrupole mechanism for a solid-state electronic transition

Abstract: Polarized high resolution absorption spectra at 4·2 K are reported for single crystals of Cs2UO2Cl4. An analysis of the polarization of the electronic origin bands and the vibronic structure provides evidence for a transition which is allowed by a pure electric-quadrupole mechanism.

Bremsstrahlung in heavy-ion reactions

Abstract: We investigate bremsstrahlung processes induced by heavy ions: nuclear dipole and quadrupole radiation, radiation from bound target electrons into the continuum and secondary electron bremsstrahlung (SEB), which contribute to the background of the X-ray spectra. A comparison with experiment is presented.

A new perturbation expansion for fluids of nonspherical molecules

Abstract: The free energy of a fluid composed of nonspherical molecules is expanded about that for a reference fluid of rigid, nonspherical molecules. The expansion procedure involved separating the intermolecular pair potential into repulsive and attractive regions for each set of relative orientations, and is similar to that used by Weeks, Chandler, and Andersen for monatomic fluids. The properties of the reference system are evaluated using the expansion of Bellemans. Calculated thermodynamic properties are compared with Monte Carlo results for fluids with a potential uLJ + ua, where uLJ is the Lennard‐Jones model and ua is either the point dipole, point quadrupole, or an anisotropic overlap potential. For dipoles, agreement is satisfactory for values of the reduced dipole moment μ/(eσ3)1/2 up to about 1, while for quadrupoles good agreement is found for Q/(eσ5)1/2 up to about 0.8. For larger multipole moments the Bellemans expansion fails. For anisotropic overlap potentials the method seemed satisfactory for al...

Analysis of57Fe Mössbauer hyperfine spectra

Abstract: It is emphasized that Mossbauer spectra of57Fe nuclei subjected to a combined magnetic dipole- and electric quadrupole interaction cannot give a unique solution for all parameters involved in these interactions, even if intensities are taken into account. Expressions are derived with which the full range of possible solutions can be calculated and we apply these to some recently published results in which the ambiguity was not recognized.