2 D Methods in NQR Spectroscopy

1992 ◽  
Vol 47 (1-2) ◽  
pp. 333-341
Author(s):  
J. Seliger ◽  
R. Blinc
Keyword(s):  
Double Resonance ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Electric Quadrupole ◽  
Quadrupole Coupling Constant ◽  
Spin Lattice Relaxation ◽  
Two Dimensional ◽  
Spin Lattice ◽  
Quadrupole Coupling ◽  
Field Cycling

AbstractThe application of two-dimensional spectroscopy to nuclear quadrupole resonance (NQR) is reviewed with special emphasys on spin 3/2 nuclei. A new two-dimensional level crossing double resonance NQR nutation technique based on magnetic field cycling is described. This technique allows for a determination of both the electric quadrupole coupling constant and the asymmetry parameter for spin 3/2 nuclei in powdered samples even in cases where the quadrupolar signals are too weak to be observed directly. It works if the usual double resonance conditions are met, i.e. if the spin-lattice relaxation times are not too short if the quadrupolar nuclei are dipolarly coupled to "strong" nuclei. Variations of this techique can be also used for 2 D "exchange" NQR spectroscopy and NQR imaging.

Deuteron Relaxation Study of the Reorienting Methyl Groups in p-Azoxyanisole

1974 ◽  
Vol 52 (12) ◽  
pp. 2294-2295 ◽  
Author(s):  
M. Wiszniewska ◽  
Ronald Y. Dong ◽  
E. Tomchuk ◽  
E. Bock
Keyword(s):  
Relaxation Times ◽  
Lattice Relaxation ◽  
Quadrupole Coupling Constant ◽  
Spin Lattice Relaxation ◽  
Isotropic Phase ◽  
Coupling Constant ◽  
Spin Lattice ◽  
Quadrupole Coupling ◽  
Relaxation Study ◽  
Deuteron Spin

The deuteron spin-lattice relaxation times were measured in the nematic and isotropic phases of p-azoxyanisole(CD3)2. An apparent activation energy for the methyl group reorientation in the isotropic phase is obtained. The quadrupole coupling constant along the C—D bond is found to be 147 ± 8 kHz.

Applications of 95Mo N.M.R. Spectroscopy. XVIII. Relaxation Times, Quadrupole Coupling Constants and Partial Field Gradients in [Mo(CO)5L] Complexes

1988 ◽  
Vol 41 (9) ◽  
pp. 1457 ◽  
Author(s):  
RTC Brownlee ◽  
BP Shehan ◽  
AG Wedd
Keyword(s):  
Relaxation Times ◽  
Lattice Relaxation ◽  
Quadrupole Coupling Constant ◽  
Coupling Constants ◽  
Spin Lattice Relaxation ◽  
Scalar Coupling ◽  
Spin Lattice ◽  
Field Gradients ◽  
Pyridine Complex ◽  
Quadrupole Coupling

A study of ,95Mo spin-lattice relaxation times (T1) and linewidths of [Mo(CO)5L] complexes, where L = PPh3, AsPh3, SbPh3, pyridine and Cl-, has shown that the relaxation times are due entirely to the quadrupolar mechanism, with no scalar coupling contribution to linewidth where molybdenum is bonded to a quadrupolar nucleus. Based on the literature value of the quadrupole coupling constant obtained by n.q.r . for the PPh3 complex (1.972 MHz), the quadrupole coupling constants of the arsine and stibine complexes are determined to be 3.36 and 3.75 MHz respectively. These values, and that of the pyridine complex (2.80 MHz), are found to correlate with ligand partial field gradient parameters obtained from Mossbauer spectra of FeII complexes, and are rationalized in terms of metal- ligand bonding interactions. For Et4N [Mo(CO)5Cl], the correlation is very poor; this result is attributed to the effects of ion in solution.

Time Domain Zero Field NMR and NQR

1986 ◽  
Vol 41 (1-2) ◽  
pp. 440-444 ◽  
Author(s):  
A. Bielecki ◽  
D. B. Zax ◽  
A. M. Thayer ◽  
J. M. Millar ◽  
A. Pines
Keyword(s):  
Time Domain ◽  
Relaxation Times ◽  
Low Frequency ◽  
High Sensitivity ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Zero Field ◽  
Spin Lattice ◽  
Field Cycling ◽  
The Time Domain

Field cycling methods are described for the time domain measurement of nuclear quadrupolar and dipolar spectra in zero applied field. Since these techniques do not involve irradiation in zero field, they offer significant advantages in terms of resolution, sensitivity at low frequency, and the accessible range of spin lattice relaxation times. Sample data are shown which illustrate the high sensitivity and resolution attainable. Comparison is made to other field cycling methods, and an outline of basic instrumental requirements is given.

17O Quadrupole Dips in Ammonium Persulphate

1994 ◽  
Vol 49 (1-2) ◽  
pp. 345-350 ◽  
Author(s):  
N. F. Peirson ◽  
J. A. S. Smith ◽  
D. Stephenson
Keyword(s):  
Relaxation Time ◽  
Lattice Relaxation ◽  
Quadrupole Coupling Constant ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Ammonium Persulphate ◽  
Spin Lattice Relaxation Time ◽  
Spin Lattice ◽  
Resonance Frequencies ◽  
Quadrupole Coupling

Abstract The magnetic field dependence of the 1H spin-lattice relaxation time in ammonium persulphate shows pronounced minima near the 1H magnetic resonance frequencies of 1,200 and 2,200 kHz. These are interpreted in terms of a model involving cross-relaxation between 1H in the NH4 ion and 17O in natural abundance in the S2O2-8 ions, the latter having a much shorter spin-lattice relaxation time. A theoretical analysis of the shape of the minima is used to derive values for the 17O quadrupole parameters. This analysis results in best estimate values for the quadrupole coupling constant of 6.75 (± 0.05) MHz and an asymmetry of 0.30 (± 0.02). Such values are indicative o f O-H hydrogen bonding and suggest the S2O2-8 ion is not undergoing rapid reorientation at temperatures below 320 K.

Nuclear Magnetic Resonance in Solid Zinc

1979 ◽  
Vol 34 (8) ◽  
pp. 1029-1030 ◽  
Author(s):  
H. Herberg ◽  
J. Abart ◽  
J. Voitländer
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Spin Echo ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Electric Quadrupole ◽  
Quadrupole Coupling Constant ◽  
Spin Lattice Relaxation ◽  
Electric Quadrupole Interaction ◽  
Nuclear Magnetic

AbstractThe nuclear magnetic resonance of 67Zn in hexagonal close-packed Zn metal has been observed at 4.2 K by pulsed NMR with three different frequencies. The spin echo profile showed a well resolved powder pattern due to electric quadrupole interaction. The quadrupole coupling constant was determined to be e2 q Q/h = 12.0 (4) MHz. The spin-spin and spin-lattice-relaxation times were measured to be T2 = 58 ± 2 ms and T1 = 0.45 ± 0.2 s, respectively. The isotropic Knight shift is found to have the value Kiso = 0.1 ± 0.05%.

Nitrogen-14 quadrupole cross-relaxation spectroscopy

1988 ◽  
Vol 416 (1850) ◽  
pp. 149-178 ◽  
Keyword(s):  
Magnetic Field ◽  
Double Resonance ◽  
Relaxation Times ◽  
High Sensitivity ◽  
Lattice Relaxation ◽  
Cross Relaxation ◽  
Spin Lattice Relaxation ◽  
Proton Relaxation ◽  
Spin Lattice ◽  
Quadrupole Resonance

Cross-relaxation spectroscopy can be used as a sensitive method of detecting 14 N quadrupole-resonance signals in hydrogen-containing solids. The 1 H spin system is polarized in a high magnetic field that is then reduced adiabatically to a much lower value satisfying the level­-crossing condition, when the 1 H Zeeman splitting matches one of the 14 N quadrupole splittings. If the 14 N spin–lattice relaxation time is much shorter than that of the 1 H nuclei, a drastic loss of 1 H polarization occurs that is measured by recording the residual 1 H magnetic resonance signal after the sample has been returned to the higher field. The experimental cycle can be run in several different ways according to the relative values of the 1 H spin–lattice relaxation times ( T 1 ) in high and low field, the 14 N spin–lattice relaxation ( T 1Q ) and cross-polarization times ( T CP ), all of which can markedly influence the spectra. The line shapes are broadened by the presence of the magnetic field and Zeeman shifts of the peak frequencies also occur, for which simple corrections may be derived. The methods used have high sensitivity, particularly if the ratio T 1 / T 1Q is large. They have the advantage over other double-resonance techniques in that long proton T 1 values are not necessary for the success of an experiment; it is also possible to select conditions in which the recovered 1 H signal is directly proportional to the relative numbers of 14 N nuclei present and the magnitude of the cross-relaxation field. Multi-proton relaxation jumps also give rise to signals at subharmonics of the fundamental, whose relative intensities reflect the extent to which the 14 N and 1 H relaxation is coupled via their dipole–dipole interactions, which are not completely quenched in the finite magnetic fields necessary in cross-relaxation spectroscopy. These conclusions are illustrated in a number of 14 N spectra of compounds in which quadrupole-resonance signals have not previously been recorded.

Sodium NMR in the trigonal phase of sodium hydrosulfide

1976 ◽  
Vol 54 (16) ◽  
pp. 1651-1659 ◽  
Author(s):  
Kenneth R. Jeffrey ◽  
Stanley L. Segel
Keyword(s):  
Phase Transition ◽  
Lattice Relaxation ◽  
Quadrupole Coupling Constant ◽  
Spin Lattice Relaxation ◽  
Trigonal Axis ◽  
Coupling Constant ◽  
Spin Lattice ◽  
Quadrupole Coupling ◽  
Nuclear Quadrupole ◽  
Trigonal Phase

Measurements of the sodium nuclear quadrupole coupling constant and spin–lattice relaxation time, while confined mainly to the trigonal phase, show the existence of the two known phase transitions at 358 and 113 K. The quadrupole coupling constant is 206 kHz at 358 K and decreases roughly linearly with decreasing temperature at a rate of about 0.66 kHz/K. The satellite peaks in the quadrupolar split powder pattern disappear above 358 K in the cubic phase. Below 130 K. where there is no known phase transition, the satellites broaden and again disappear but in this case it is because the fluctuation rate of the electric field gradient at the sodium site due to reorientation of the SH− ion is about equal to the quadrupolar splitting of the spectrum at this temperature. Only the resonance from the −1/2 ↔ 1/2 transition is observed down to 77 K.The spin–lattice relaxation of the sodium spins shows a very strong temperature dependence and a well-defined minimum similar to the previously observed results for the protons. The relaxation is caused by the nuclear quadrupole interaction made time dependent by the reorientation of the neighbouring SH− ions. A simple model calculation gives reasonable agreement between the calculated and experimental values of T1 at the minimum if the SH− ion is considered to move between two positions parallel and antiparallel to the trigonal axis. An extension of this model suggests that the lack of an enhanced relaxation rate at the 113 K phase transition may be a result of a parallel ordering of neighbouring SH− ions along the trigonal axis in the lowest temperature phase.

Reorientational Motion of Hydrogen Bonded Octahedral Complex Anions in Hydrazinium Hexachlorostannate(IV), (N2H5)2SnCl6, as Studied by 35Cl NQR Spin-Lattice Relaxation Measurements

1992 ◽  
Vol 47 (1-2) ◽  
pp. 288-292
Author(s):  
Yoshio Kume ◽  
Maki Tokoro ◽  
Tetsuo Asaji ◽  
Ryuichi Ikeda ◽  
Daiyu Nakamura
Keyword(s):  
Relaxation Times ◽  
Lattice Relaxation ◽  
Electric Quadrupole ◽  
Positive Temperature Coefficient ◽  
Wide Frequency Range ◽  
Spin Lattice Relaxation ◽  
Octahedral Complex ◽  
Positive Temperature ◽  
Electric Quadrupole Interaction ◽  
Spin Lattice

AbstractThe temperature dependences of NQR frequencies and spin-lattice relaxation times, T1Q, of 35Cl in (N2H5 ) 2SnCl6 were measured. Four NQR signals distributed in a fairly wide frequency range were observed, the lowest-frequency line exhibiting an anomalous positive temperature coefficient. The highest-frequency line showed a steep temperature dependence. These results could be interpreted by considering the intermolecular interaction between CI and - NH2 in N2H5+ . Below ca. 250 K, T1Q of the upper three signals exhibited a gradual decrease upon heating, explainable by lattice vibrations, while a shallow T1Q minimum, ascribable to the modulation of electric quadrupole interaction, was observed at ca. 110K for the lowest-frequency signal. The reorientation of [SnCl6]2- was elucidated to be highly anisotropic, in that it reorients about one of the CI-Sn-Cl axes much more frequently than about the other two axes. The activation energies were determined to be 62 and 94 kj mol -1 for the respective reorientations.

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