Nuclear Quadrupole Research Articles

The Iodine Hvperfine Structure in the Microwave Spectrum of Ethyl Iodide: Nuclear Quadrupole and Spin Rotation Coupling

Abstract Some rotational transitions of ethyl iodide, CH3CH2I, have been reinvestigated by microwave Fourier transform (MWFT) spectroscopy. The iodine hyperfine structure splittings were first ana lyzed using a direct diagonalization procedure of the complete quadrupole Hamiltonian matrix. The results of this analysis showed deviations from our measurements up to 60 kHz. A new analysis using additional spin rotation coupling matrix elements reproduces our measurements within the experi­mental error limit and decreases the standard deviation of the least squares fit from 28 kHz to only 4 kHz.

A simple microscopic approach to the nuclear giant monopole and quadrupole resonances

The monopole and quadrupole excitation modes of spin-saturated nuclei are studied by means of sum rules, using a simple density-dependent finite-range interaction with particular emphasis on the effects of the finite range of the interaction on the excitation energies. Within the framework of the density matrix expansion, it is shown that the excitation energies can be related to the various contributions coming from the total energy of a nucleus. This approach has the advantage of separating out of part from the relations of the excitation energies which exists only for a finite-range interaction and vanishes for zero-range interactions of the Skyrme type.

Nuclear quadrupole optical hole burning in stoichiometric EuAsO4

The intrinsic site and over forty defect sites have been studied by optical absorption, fluorescence and optical hole burning in EuAsO4. The hole-burning spectra have allowed determination of the nuclear electrical quadrupole parameters P and asymmetry parameters eta for the 5D0 levels for both Eu isotopes at 11 of these sites. A model is presented that explains the observed correlation between the P-values and the electronic energy shifts of the defect sites. Nuclear Zeeman effect studies of two sites using nuclear hole-burning spectroscopy in fields up to 8.8 T have allowed the determination of the orientation of their 5D0 electronic quadrupole tensors. Reasonable connection is made with two types of localised defect that are expected to occur frequently in the lattice structure. Energy transfer effects have also been examined as a function of temperature.

ChemInform Abstract: Microwave Spectrum and 14N Quadrupole Coupling Constants of Indole.

Abstract The microwave spectrum of indole has been observed using a conventional Stark-modulated microwave spectrometer in conjunction with a heated absorption cell. Spectral transitions were also observed in a pulsed molecular beam Fabry-Perot microwave spectrometer using a heated nozzle source. The high resolution (20 kHz) available with the Fabry-Perot instrument allows the observation of the 14N nuclear electric quadrupole hyperfine splittings. An analysis of the 44 measured transitions gives the following rotational constants: A = 3877.8366(64) MHz; B = 1636.0461(48) MHz; and C = 1150.0900(19) MHz. The 14N quadrupole coupling constants that were determined from the hyperfine analysis are eQqaa = 1.7263(43) MHz; eQqbb = 1.6525(50) MHz; and eQqcc = −3.3788(48) MHz. The observed rotational constants are compared with those obtained from a recent optical study of indole and the 14N quadrupole coupling constants are compared with those of pyrrole.

Nuclear relaxation and Knight shift studies of 63Cu in 90 K-and 60 K-class YBa 2Cu 3O 7−y

The nuclear relaxation rate (1/T 1) and Knight shift for Cu of YBa 2Cu 3O 7−y were measured by using the nuclear quadrupole (NQR) and magnetic resonance (NMR) techniques. For 90 K-superconductor with y∼o, 1/T 1 at the CuO 2 plane site decreases markedly without the enhancement just below T c and approximates to a T 3 behavior between 40K and 10 K. Knight shift shows a distinct decreases below T c, giving an evidence for dominant singlet pairing. For an explanation of unconventional nuclear relaxation behavior, it seems plausible to apply a d-wave model with the gap zeros of lines on the Fermi surface. For 60 K-superconductor, we found a surprising result that 1/T 1 at the CuO 2 plane site is by three order of magnitude suppressed as compared to that of 90 K superconductor and shows no anomalies at T c= 60K. This marked difference of relaxation behaviors between 90K and 60K superconductors implies a strong correlation with the mechanism of high T c superconductivity.

Nuclear Relaxation and Knight Shift Studies of Copper in YBa2Cu3O7-y

The nuclear relaxation rate 1/ T 1 and the Knight shift have been studied for boththe Cu–O plane and chain sites by Cu nuclear quadrupole (NQR) and magnetic resonance (NMR) techniques. Below T c =92 K, 1/ T 1 for the plane site decreases markedly without the enhancement just below T c characteristic for the BCS superconductor, and the Knight shift also shows a more rapid reduction than the BCS prediction, giving evidence of a dominant singlet pairing. In contrast, 1/ T 1 for the chain site shows a weak temperature dependence below T c . This difference of the 1/ T 1 behavior for the plane and chain Cu sites is attributed to the difference of the relaxation processes, i.e., the magnetic and quadrupole relaxation processes, respectively. From both the behaviors of 1/ T and the Knight shift at the plane site, it is pointed out that the Cooper pair may be of a d-type formed by a strong coupling with a large energy gap.

Magnetism of Eu(BrO 3) 3·9H 2O and the crystal field

Crystals of hydrated europium bromate were grown and magnetic susceptibilities measured from room down to liquid oxygen temperatures. The effective magnetic moment p eff is found todecrease with decreasing temperature indicating a Van Vleck high temperature contribution. The magnetic anisotropy Δ χ= χ‖− χ ⊥ is negative and appreciable. The magnetic susceptibilities χ ‖; and χ ⊥ parallel and perpendicular to c-axis, respectively, rise slowly with decreasing temperature, and around 115 K χ ⊥ becomes nearly constant while χ ‖ decrease slightly; this is quite in contrast to the behavior of other rare earth bromates. A crystal field conforming to D 3h symmetry provided a satisfactory explanation to the observed magnetic behavior. The crystal field parameters used are B 20=175, B 40=−304, B 60=−864 and B 66=910 all in cm −1. The Schottky heat capacity C s does not display any anomaly and vanishes below 50 K. Nuclear quadrupole and magnetic hyperfine splitting due to the crystal field has been worked out. The hyperfine heat capacity for both isotopes shows Schottky anomaly below 2 mK.

General solution to axially symmetric quadrupole interaction in nuclear magnetic resonance of solids

Spins with magnitude I greater than [Formula: see text] have nuclear electric quadrupole interactions that perturb the Zeeman splitting. To calculate the spin dynamics of multipulse sequences, it is necessary to know how the system evolves between pulses under the quadrupole. Prior work gave specific solution for [Formula: see text] in tabulated form. In this paper, a single expression is obtained, which is valid for all.I.

Enhanced nuclear order in HoVO4revisited: II. Zeeman effects in the nuclear quadrupole resonance of51V

For pt. I see ibid., vol.20, p.797 (1987). The second-order Zeeman shift in the nuclear electric quadrupole resonance at 993.4 kHz of 51V in HoVO4 is used to probe the enhanced nuclear antiferromagnetic ordered state of the 165Ho moments below 5 mK.

High-resolution calcium-43 NMR in solids

The resolution afforded by alkaline earth ion NMR in solution is often insufficient to obtain individual lines for chemically distinct sites, particularly in macromolecular environments (Z-4). The problem inherent in a small chemical shift range of about 70 ppm is aggravated further by broadening associated with the often complex spin relaxation driven by the nuclear electric quadrupole interactions with fluctuating electric field gradients (5). The dynamical part of the broadening may be defeated if the nucleus to be observed is immobilized. The solid-state experiment has been successful on a number of nonintegral spin quadrupole nuclei where the central (+f c-) -1) transition is exploited and the residual second-order quadrupole broadenings are minimized by rapid sample rotation at the magic angle (6-9). However, the possible gain in resolution is made at the cost of decreased sensitivity because only the central transition in a ; or $ manifold is observed (IO). In principle, the loss may be regained using magnetization-transfer methods such as those exploited by Pines, Gibby, and Waugh (II). Double-resonance approaches have been discussed for calcium fluoride (12,13), and a direct detection of calcium-43 reported using adiabatic demagnetization methods at low temperature (14). We report here observation of the high-resolution calcium-43 NMR spectrum using CP-MASS methods which demonstrates the feasibility of the more routine experiment in a noncubic environment and defines several of the critical experimental parameters. Figure 1 shows the CP-MASS calcium-43 NMR spectrum of calcium acetate obtained at 4.7 T using a spectrometer constructed in this laboratory. The relevant experimental parameters are summarized in the caption. The proton-calcium doubleresonance probe employed a Doty Scientific stator and rotor coupled to the proton tuning elements using a half wavelength coaxial line tapped at the proton null point for injection and detection of the calcium-43 resonance frequency. The spectrometer used Amplifier Research (AR-200L) and Henry Radio power amplifiers, Nicolet-GE 1280 data system, and a quadrature receiver built in the laboratory. The phase-shifting circuitry was designed after a very similar version by Robert MacKay, Monsanto Chemical Company. The match for the magnetization transfer was found by changing the power level on the calcium side while keeping the proton field fixed at 46 kHz; the optimum cross-polarization rate was found when the strength of the calcium rf field was approximately the same as that which gave w1 for calcium of 45 kHz in a saturated aqueous solution of calcium chloride. For calcium acetate, optimum contact times were long, in the tens of milliseconds range as shown in Fig. 2.

The lengthening of the HF bond on formation of heterodimers B • • • HF: determination and dependence on the strength of the hydrogen bond

We report a procedure that for the first time allows the quantitative determination of the lengthening δr of the HF bond on formation of an isolated hydrogen-bonded dimer B···HF. We show how δr can be obtained from the ground-state hyperfine coupling constants X (D nuclear quadrupole) and D HF (H, F nuclear spin to nuclear spin), which are available from the rotational spectra of the molecules B···H(D)F. We establish the values of δr for the series of heterodimers B···HF where B = Ar, Kr, Xe, N 2 , CO, H 2 S, HCN, CH 3 CN and H 2 O. The values of δr are zero for the first three members of this series and then 0.001, 0.007, 0.010, 0.014, 0.016 and 0.015 Å, respectively (1 Å = 10 -1 nm = 10 -10 m). It is found that δr is a monotonically increasing function of the hydrogen-bond stretching force constant k σ , which is taken as a convenient measure of the hydrogen bond strength.

The extraction of weak nuclear electric quadrupole splittings of dilute impurities in ferromagnets using modulated Adiabatic Passage NMR/ON

A novel extension of the Single or Adiabatic Fast Passage NMR/ON technique is described. Its principal advantages in extracting the mode magnitudes and distribution widths of weak nuclear electric quadrupole splittings much less than the magnetic inhomogeneous broadening are its simplicity and generality requiring no assumptions on the degree of adiabaticity of the nuclear spin motion during sweep through the quadrupolar split subresonances. The technique is applied to a concentrated single crystal sample of60CoFe which failed to yield a well resolved mid passage signal to conventional single passage NMR/ON. The result is an asymmetric frequency distribution of quadrupole frequencies with a mode value of P=3e2qQ/4I (2I-1)=+4.5 ±1.0 kHz and half maxima of +2.5 kHz and +7.0 kHz.

Molecular Electric Quadrupole Moment, Magnetic Susceptibility Tensor and Deuterium Quadrupole Coupling Constant in Cyanoacetylene

The rotational Zeeman effect in the J → J′ = 0 → 1 and 1 → 2 rotational transitions has been observed for H-C≡C-C≡14N, D-C≡C-C≡14N, D-C≡C-C=15N, and H-C≡C-C=I5N using a microwave bridge superheterodyne spectrometer. From the experimental g⊥-values, susceptibility anisotropies and rotational constants, the molecular electric quadrunole moment, which plays an important role for collisional excitation and relaxation, follows as Q∥=2.14(9) x 10-26esu cm2 (referred to the center of mass of the H-C≡C-C≡14N species). Since the Deuterium quadrupole hyperfine splittings in the Zeeman spectra could be resolved, it was also possible to Fit the Deuterium quadrupole coupling constant. Our value, eqQ (2H) = 198.2(46) kHz is about 10% smaller than the value derived from a recent high resolution microwave Fourier transform study. The reasons for this discrepancy are discussed. All experimental molecular parameters are compared to the results of ab initio quantum chemical calculations and it is argued that the 14N nuclear electric quadrupole moment is possibly about 30% larger than presently assumed.

Semiempirical Sternheimer shielding factors for the atomic4fand5dshells

Sternheimer shielding factors are often obtained empirically by comparing nuclear electric quadrupole moment values derived from the hyperfine structure (hfs) of many-electron atoms with those determined by Coulomb-excitation or mesic-atom measurements. A large scatter in the resulting shielding factors arises from the lack of consistency in the approaches used in the analyses of the hfs. In the present work the radial hfs integrals are evaluated with a consistent configuration-average Dirac-Fock method. The scatter in the shielding factors obtained is reduced substantially and the results are in reasonable agreement with Sternheimer's original estimates.

Nuclear quadrupole and magnetic resonance studies of structure and the molecular motion in SYM C6Cl 3F 3

35Cl and 19F relaxation time measurements were carried out on sym C 6Cl 3F 3. The analyses of the 19F high-resolution NMR spectra and the 35Cl spin-lattice relaxation time showed that the crystal belongs to a trigonal or a hexagonal crystal system in which the molecules undergo three-fold reorientation about the molecular figure axis with the correlation time τ c/s=3.42·10 −7 exp(18.2 kJ mol −1/ RT). Temperature dependences of the 35Cl NQR frequency and 19F spin-lattice relaxation times are such that only a minor structural change is associated with the phase transition at 296 K.

ESR of Eu2+in X-irradiated CaSO4:Eu3+

A detailed ESR analysis of Eu2+ centres in CaSO4, produced by X-irradiation of CaSO4:Eu3+ single crystals, has been carried out at 295K using microwave frequencies of 36.5 and 9.2 GHz. The spectra can be described by an orthorhombic spin Hamiltonian and show effects due to large magnetic hyperfine, nuclear quadrupole and nuclear Zeeman interactions it is shown that the bonding at the Eu2+ site has a significant covalent contribution. The observed Eu2+ centres are produced by the reduction of those Eu3+ ions that replace Ca2+ substitutionally and that are not locally charge-compensated.

14N and 35Cl double resonance study of the phase transition in the intercalated bilayer compound C10H21NH3Cl

The pure nuclear quadrupole (NQR) spectra of 14N, 35Cl, and 37Cl have been measured in C10H21NH3Cl as a function of temperature. The chlorine NQR frequency νQ (35Cl)=1215 kHz at 47 °C is determined by the N–H––Cl hydrogen bonds and is the lowest reported so far. The 14N quadrupole coupling data e2qQ/h=760 kHz. η=0 shows that the C–N–H––Cl backbone is practically rigid at this temperature. Above 53 °C the effects of the phase transition from an intercalated to a nonintercalated structure show up in the N–H––Cl backbone as a sharp drop of the NQR frequencies to ∼60% of their rigid lattice values. A model accounting for this effect has been proposed.

Nuclear magnetic resonance of51V (I=7/2) in lanthanide vanadates: I. The paramagnetic shifts

Nuclear magnetic resonance of 51V (I=7/2) has been studied at temperatures down to 1.5K in single crystals of lanthanide vanadates LnVO4 where Ln3+ ranges from Pr3+, 4f2 to Yb3+, 4f13. The crystals are tetragonal, four molecules per unit cell, but all V5+ sites and all Ln3+ sites are magnetically equivalent. Measurements are made with applied fields parallel and perpendicular to the tetragonal axis, and fitted to the spin-Hamiltonian H=- gamma //h(cross)BzIz- gamma perpendicular to h(cross)(BxIx+ByIy)+P(Iz2-1/3I(I+1)). Values for the paramagnetic shifts are used to deduce the local fields at both the V5+ and Ln3+ sites. These fields are compared with the dipolar values, from which the magnitude of the transferred hyperfine interaction at the V5+ sites is deduced, together with estimates of the exchange interaction between the Ln3+ ions. The nuclear electric quadrupole interaction for 51V is discussed in paper II, and measurements in the antiferromagnetic phases of GdVO4 and DyVO4 in paper III.

Determination of the complete14N quadrupole interaction tensor in a photoexeited triplet state by zero and low field optically detected ENDOR Application to NaNO2/Ag

The optically detected E.S.R. and ENDOR spectra at zero field and low fields of the triplet state of the major NO2 − trap in NaNO2 doped with AgNO2 are presented and analysed. The fine structure and complete 14N nuclear hyperfine and quadrupole interaction tensors are obtained for the trap triplet state. The results are shown to be consistent with an assignment of the trap triplet state as 3 B 1, localized on a NO2 − ion and arising from a π(b 1)←σ(a 1) orbital excitation. The cation (Ag+ and Na+) interactions are observable, but small.

Magnetic resonance in a cubic Ґ 3 (E) doublet system IV. Improved theory of the nuclear interactions

In previous papers of this series, a study has been made of the theory of magnetic resonance in a Ґ 3 doublet (paper I), together with experimental studies of Cs 2 NaHoCl 6 by n. m. r. (paper II) and by e. s. r. (paper III). In this substance the Ho 3+ ion, 4f 10 , 5 I 8 , is in an octahedral crystal field which gives a Ґ 3 doublet as the ground electronic state. The results, both from enhanced n. m. r. of the 165 Ho nucleus ( I = 7/2) and from e. s. r., provide evidence of fast motional averaging, ascribed to interactions between the ions. The measurements are in substantial agreement with the theory of I; however, though the theory is correct for the electronic levels and transitions, and for the nuclear electric quadrupole interaction in zero magnetic field, it needs improvement in the treatment of the nuclear terms when a field B is applied. In this paper a general theory is developed for the case when B is in an arbitrary direction, together with some special cases that are analytically simpler. These include B along [111], the spectrum of an isolated ion, and the spectrum of a concentrated compound where there are fast flip-flops between the electronic states.