Nuclear quadrupole resonance

About: Nuclear quadrupole resonance is a research topic. Over the lifetime, 3531 publications have been published within this topic receiving 38801 citations. The topic is also known as: Nuclear quadrupole resonance spectroscopy & NQR.

Zeeman nuclear quadrupole resonance line shapes in powders (I = 3/2)

Abstract: Theoretical absorption line shapes are presented for Zeeman perturbed nuclear quadrupole resonance transitions (I = 3/2) in polycrystalline materials for the case in which the rf field is parallel to the Zeeman field. For a nuclear spin of 3/2, the pure quadrupole transition frequency νQ(1+η2/3)1/2 is insufficient to independently determine either νQ, the strength of the quadrupole interaction, or η, the asymmetry in the electric field gradient tensor. Application of a magnetic field removes the degeneracy of the energy levels producing, in general, four orientation dependent transition frequencies from which the quadrupole parameters can be determined. Computer simulated powder lineshapes are presented which are exact in η and are to first order in applied magnetic field strength. Frequencies of the features of the line shape are plotted as a function of η. The features of the line shape are due to crystallites aligned such that the applied field is parallel to one of the principal axes of the electric f...

Secondary echoes in three-frequency nuclear quadrupole resonance of spin-1 nuclei

Abstract: We demonstrate, theoretically and experimentally, that the irradiation of a powder sample containing spin-1 nuclei by two of the three characteristic nuclear quadrupole resonance (NQR) frequencies can result in several echo signals at the third NQR frequency. One of these echoes, the principal echo, has the same shape and time of occurrence as an echo produced after a pair of single-frequency excitations. The other echoes are not equivalent to any single-frequency echo. These secondary echoes are the focus of this paper. The time of occurrence and shape of the secondary echoes are determined by the correlation of the distribution in one transition frequency to the distribution in a second transition frequency. This correlation is in turn determined by the correlation between the distributions of the electric field gradient components, which is itself determined by the types and concentrations of crystalline defects present. We present the optimal conditions to observe such secondary echoes and compare theory with experiment using 14N (I=1) in powder samples of sodium nitrite and RDX.

Halogan nuclear quadrupole resonance in tetrahedral halo complexes of zinc

Abstract: Halogen nuclear quadrupole resonance data are presented for a number of compounds containing tetrahedral ZnX42- ions, where X = Cl, Br, and I. Characteristic mean frequencies are: for 35Cl in ZnCl42- 8.9 MHz ; for 81Br in ZnBr42- 60 MHz; and for 127I in ZnI42- 75 and 150 MHz. The number and relative intensities of the resonances for any compound is found to be a useful indication of the site symmetry of the ZnX42- ion, and compounds of unknown structure are examined in this light. 35Cl data are also presented for Cs2CuCl4, which has a mean frequency of 10.6 MHz at 298°K.

Charge transfer to the local singlet states as a function of Li content in La2Cu1−xLixO4 and La1.85Sr0.15Cu1−xLixO4

Abstract: Magnetic susceptibility (χ) and NMR/NQR measurements were performed on La2Cu1−xLixO4 0≤x≤0.5) and La1.85Sr0.15Cu1−xLixO4 (0≤x≤0.425). The narrow 63Cu NQR line at νQ = 46.3 MHz (1.3 K) is detected in La2Cu0.5Li0.5O4. This frequency is higher than all 63Cu-NQR frequencies found so far in all the cuprates. Moreover, a further increase of νQ is observed in the solid solutions La2Cu1−xLixO4 with decreasing x. Corresponding electric field gradients (EFG's) are considered in terms of ionic and cluster models. The 3d hole density nx2−y2 ≈ 1 and the radial average 〈r−3〉 ≈ 9.5 a.u. are derived from the EFG's, suggesting the d9 L state of the formally trivalent copper. The antiferromagnetic ordering is rapidly suppressed as a function of x in the La2Cu1−xLixO4, and for x ≥ 0.03 we find TN ≈ 0. The evolution of χ vs. x shows a gradual decrease of Cu spin susceptibility and its disappearance in the diamagnetic La2Cu0.5Li0.5O4, in which χ = −6.7 × 10−5 cm3/mole is composed of Van Vleck and core terms. The electronic state is implied to be a local singlet (1A1g) of primarily d9 L character. The quadrupole signature of the local singlet in the range 46.3 ≤ 63 ν Q ≤ 47.0 MHz is observed for x > 0.15 in both systems, La2Cu1−xLixO4 and La1.85Sr0.15Cu1−xLixO4. The differentiation of charge between local singlet and conductivity band states is discussed.

H-14N double resonance of TNT from a land mine

Abstract: The 14 N NQR spectrum of one gram of military grade trinitrotoluene (TNT) obtained from an abandoned land mine has been determined by 1 H- 14 N nuclear quadrupole double resonance at room temperature. The magnetic field dependence of the proton spin-lattice relaxation time T 1 as well as the 14 N T 1 of TNT were determined as well. The use of a double frequency irradiation technique allowed for a unique assignment of the twelve observed lines to the v + and v- 14 N transitions of the six chemically non-equivalent crystallographic nitrogen sites in the unit cell. Nuclear quadrupole double resonance results in an increase in the 14 N signal to noise ratio by a factor of 30 as compared to conventional NQR and a significant reduction of the measuring time which is important in the detection of explosives.