Showing papers on "Nuclear quadrupole resonance published in 1980"
TL;DR: In this article, the pulsed spin locking in NMR has been applied to a pure NQR system, with results very similar to those obtained in the NMR case, however, the theoretical methods used to explain the NRT results are not applicable to the pure NRT case.
Abstract: The technique of pulsed spin locking in NMR has recently been applied to a pure NQR system, with results very similar to those obtained in the NMR case. However, the theoretical methods used to explain the NMR results are not applicable to the pure NQR case. Using a model of the NQR system, a method is developed for following its evolution, which leads to results which reproduce the experimentally observed short‐time behavior, and which are in some agreement with the long‐time behavior.
71 citations
44 citations
TL;DR: In this article, the authors investigated the photostructural effects in 300K substrate evaporated films of As2S3 and As2Se3 using nuclear quadrupole resonance (NQR) techniques.
Abstract: Photostructural effects are investigated in 300K substrate evaporated films of As2S3 and As2Se3 using nuclear quadrupole resonance (NQR) techniques. NQR results confirm the existence of As2S4 (or As4Se4) molecular units in the films and suggest the presence of AsS3 (or AsSe3) pyramidal units which lack the longer range (two-dimensional) correlations present in the bulk. Structural differences between film and bulk are greater (and photostructural changes are easier to induce) in As2S3 than in As2Se3.
42 citations
37 citations
TL;DR: In this paper, an infrared-radiofrequency double resonance inside a CO 2 N 2 O laser cavity has been applied to the observation of pure nuclear quadrupole resonance and direct A 1 - A 2 transitions of CH 3 Br.
36 citations
TL;DR: In this article, a new technique was described for the detection of the nuclear quadrupole resonance of rare nuclei in powdered solids and frozen liquids using only small-amplitude radio-frequency fields (∼10−4T) very high sensitivities are obtained in suitable specimens such that the NQR of 17O in natural abundance (0.037%) is detected with ease.
35 citations
TL;DR: In this paper, a general, explicit, and closed-form solution for the NQR I = 1 eigenvalue problem was developed for an arbitary magnitude of the asymmetry parameter (n) and strength and orientation of the Zeeman field.
Abstract: A general, explicit, and closed‐form solution is developed for the general NQR I=1 eigenvalue problem that is valid for an arbitary magnitude of the asymmetry parameter (n) and strength and orientation of the Zeeman field.(AIP)
32 citations
TL;DR: In this paper, double resonance with coupled multiplets (D.R.C) was used for detecting nuclear quadrupole resonance (N.Q.R) in polycrystalline hexagonal Ice ac 77 K.
26 citations
TL;DR: In this paper, the phase transitions in Cu3SbS3 were investigated under temperature variation using X-ray diffraction and nuclear quadrupole resonance (NQR).
25 citations
TL;DR: In this article, the Zeeman effect on the higher lines was examined by using single crystals in order to deduce the asymmetry parameters of the electric field gradient tensor, which were found to be 0.29, 0.31, and 0.33 for X=Cl, Br, and I, respectively.
22 citations
TL;DR: In this article, the crystal structure of the intermediate phase is reported and compared with a previous determination of the high-temperature phase, where the unit cell dimensions of the two structures are almost identical and the space groups are Ptextdecoration:overline1 and P21/n, respectively.
Abstract: Previous studies using nuclear quadrupole resonance and calorimetric methods have shown that there are two second-order phase transitions in malononitrile at 141 and 294.7 K and that the low- and high-temperature phases have the same symmetry. In this paper the crystal structure of the intermediate phase is reported and compared with a previous determination of the high-temperature phase. The unit cell dimensions of the two structures are almost identical and the space groups are Ptext-decoration:overline1 and P21/n, respectively. The structures are related by relative translations and rotations of the molecules and this motion is identified with the eigenvector of the soft mode associated with the transition. The basis of a theory for such a system is developed using the quasi-harmonic approximation.
TL;DR: In this article, it was found that the NQR line shape of a-As is highly asymmetric, and this asymmetry was attributed to a distribution of dihedral angles.
Abstract: Pulsed nuclear quadrupole resonance (NQR) experiments have been performed on three forms of elemental arsenic: amorphous (a), rhombohedral (rh), and orthorhombic (or). The temperature dependence of the spin-lattice relaxation time (T/sub 1/) provides evidence for the existence of disorder (tunneling) modes in a-As. It is found that the NQR line shape of a-As is highly asymmetric, and this asymmetry is attributed to a distribution of dihedral angles in a-As. The observed NQR frequencies indicate that the amount of bonding s admixture is different in each material (rh-As:3%, or-As:7%, a-As:10%). Simple calculations in comparison with x-ray results indicate that the bonding configurations in these three forms of arsenic do not necessarily correspond to maximum overlap of bonding orbitals on adjacent atoms.
TL;DR: In this article, the nuclear quadrupole resonance (NQR) spectra of 22 monosubstituted anilines were analyzed in the framework of the Townes and Dailey theory.
Abstract: 14N nuclear quadrupole resonance (NQR) spectra of 22 monosubstituted anilines are reported and analyzed in the framework of the Townes and Dailey theory. Satisfactory correlations of the NQR data with both the Hammett σ parameters and the in vitro biological activities of the corresponding sulfanilamides have been found. The results obtained suggest that the nitrogen lone-pair orbital is more sensitive than the nitrogen–carbon sigma orbital is to substituent effects.
TL;DR: In this article, the effect of hydrogen bonding on the electric field gradient asymmetry parameter η was investigated at room temperature in polycrystalline samples of 2,6, 2,5 and 3,5-dichlorophenol.
Abstract: The Zeeman effect of chlorine nuclear quadrupole resonance in polycrystalline samples of 2,6-, 2,5 and 3,5-dichlorophenol has been investigated at room temperature in order to study the effect of hydrogen bonding on the electric field gradient asymmetry parameter η. While the two n.q.r. lines in 3,5-dichlorophenol gave an asymmetry parameter of ≈ 10%, those in 2,6- and 2,5-dichlorophenol gave different values of η for the two chlorines. The chlorine atom which is ortho to the OH group and involved in hydrogen bonding (i.e., corresponding to the low frequency line) gave an asymmetry parameter of 0.21 in 2,6-dichlorophenol and 0.17 in 2,5-dichlorophenol while the other chlorine (i.e., corresponding to the high frequency line) gave a lower value of 0.12 in 2,6-dichlorophenol and 0.11 in 2,5-dichlorophenol. These values of η are discussed in terms of hydrogen bonding and bond parameters.
TL;DR: In this paper, a design for a circuit that produces an accurately bi-symmetric modulating field of variable frequency amplitude and mark-to-space ratio with sufficient power for most NQR applications including nitrogen resonances in field gradients of high asymmetry is given.
Abstract: A design is given for a circuit that produces an accurately bi-symmetric modulating field of variable frequency amplitude and mark-to-space ratio with sufficient power for most NQR applications including nitrogen resonances in field-gradients of high asymmetry.
TL;DR: In this article, a study of the chlorine nuclear quadrupole resonance spectrum of K2OsCl6 in the vicinity of the structural phase transition using Fourier transform techniques is reported, showing that at high temperatures a single symmetric line spectrum is observed as expected from the high temperature cubic antifluorite structure.
Abstract: A study of the chlorine nuclear quadrupole resonance spectrum of K2OsCl6 in the vicinity of the structural phase transition using Fourier transform techniques is reported. At high temperatures a single symmetric line spectrum is observed as expected from the high temperature cubic antifluorite structure. Below Tc = 45 K the two symmetric line spectrum characteristic of a tetragonal distortion is seen. At intermediate temperatures, 45 < T < 150 K the spectrum consists of a single asymmetric line. A detailed analysis reveals that for the single crystal sample the asymmetric line is composed of two symmetric components, a main line, and a weak satellite shifted −1.5 kHz relative to the main line. This feature is unaffected by changes in temperature near Tc. It is attributed to the influence of interstitial impurities on neighbouring chlorine ions. For the powder sample, the asymmetry is qualitatively different. A detailed analysis shows that the line is a superposition of three components. In addition to the...
TL;DR: In this article, the authors present a review of the use of the Harcmann-Hahn equation to detect double resonance signals in polycrystalline solids with the isotope in its natural abundance (0.0037%).
TL;DR: The 14N nuclear quadrupole resonance spectra of alloxan·H2O have been observed at room temperature and the predominant tautomer in a solid is concluded to be 5,5-dihydroxypyrimidine-2,4,6-trione as mentioned in this paper.
Abstract: The 14N nuclear quadrupole resonance spectra of alloxan·H2O have been observed at room temperature. The predominant tautomer in a solid is concluded to be 5,5-dihydroxypyrimidine-2,4,6-trione. The NQR data were interpreted qualitatively by means of the Townes and Dailey theory.
TL;DR: In this paper, the origin of dis-tortion from square planarity (D4h) of the ICl4 ion is discussed in terms of secondary bonding interactions in the solid state.
Abstract: Two crystal modifications of [SCl3][ICl4] have been characterised by elemental analysis, and Raman and n.q.r. spectroscopy. Analysis of the spectra indicates that both form I (stable) and form II (metastable) involve dis-tortion from square planarity (D4h) of the ICl4– ions, a conclusion independently confirmed recently by an X-ray diffraction study of form I. On the basis of the Raman and n.q.r. spectra, the distortion in form II is similar to that observed in Na[ICl4]·2H2O. The origins of these distortions are discussed in terms of secondary bonding interactions in the solid state.
TL;DR: In this article, the authors observed the 81Br NQR of several molecular complexes of AlBr3 with amines such as (CH3)3N, C5H5N, and C6H5NH2.
Abstract: We observed the 81Br NQR of several molecular complexes of AlBr3 with amines such as (CH3)3N, C5H5N, C6H5NH2, and (C6H5)2NH All the 81Br resonance lines were found in the frequency range of 78–86 MHz at room temperature except for AlBr3·2C5H5N From the Zeeman analysis, it was proved that AlBr3·2C5H5N should be expressed with the molecular formula 2AlBr3·4C5H5N and contains cation species AlBr2(C5H5N)4+ with two 81Br resonance lines near 70 MHz and anion species AlBr4− with four 81Br resonance lines near 80 MHz The two 81Br resonance lines of AlBr3·(CH3)3N disappeared at about 40 °C due to hindered rotation of the whole molecule The lower two 81Br resonance lines of AlBr2(C5H5N)4+ have positive temperature coefficients
TL;DR: In this paper, the NQR spectra of a quadrupole resonance (NQR) was used to estimate the population of the nitrogen donor orbital directed toward the metal ion or other Lewis acid.
TL;DR: In this article, the authors examined the spectral properties of the chlorine-35 n.q.r. spectra for α-(NSClO)3, cis-(NSCLO)2(NPCl2), and (NPClO)(NPCl 2)2 in the temperature range 77-300 K. The NSClO group is more electronegative than the NPCl2 group, and the corresponding relationships are ϕ=−0.0345ν+ 8 for P-Cl bonds and ϕ = −0.0265ν+8
Abstract: Chlorine-35 n.q.r. spectra for α-(NSClO)3, cis-(NSClO)2(NPCl2), and (NSClO)(NPCl2)2 have been recorded in the temperature range 77–300 K. Spectra have also been examined for these substances at 293 K when subjected to pressures within the range 1–700 kg cm–2 : the chlorine-35 resonance frequencies are linear functions of pressure. The partial differential coefficients (∂ν/∂P)T at 293 K, (∂ν/∂T)P, at 1 kg cm–2 and 293 K, and (∂ν/∂T)v, at 293 K have been evaluated for each resonance frequency and are related to the molecular conformers present in these solids. At 165 K (NSClO)(NPCl2)2 undergoes a phase change in which the conformation of the six-membered ring changes. The chlorine resonance frequencies, ν/MHz, are related to the corresponding bond lengths, d/A: these relationships are d=–0.0152ν+ 2.4166 for P–Cl bonds and d=–0.0172ν+ 2.636 for S–Cl bonds. The NSClO group is more electronegative than the NPCl2 group. Chlorine valence-electron populations, ϕ, can be deduced from the corresponding chlorine-35 n.q.r. frequencies at 77 K. The appropriate relationships are ϕ=–0.0345ν+ 8 for P–Cl bonds and ϕ=–0.0265ν+ 8 for SClO groups.
TL;DR: In this paper, electric field gradients at the arsenic sites in the GaAsAlAs mixed compounds are calculated using the self-consistent pseudo-potential method, which is in good agreement with recent nuclear quadrupole resonance (NQR) experiments and supports the interpretation that the NQR splittings arise from an Al ion relacing one of the four Ga ions near an As site.
TL;DR: Magnetic ordering and Kondo behavior have been studied in CeAl 2 using 27 Al NQR as discussed by the authors, and spin-lattice relaxation rates indicate inhomogeneous activated-magnon and kondo-like fluctuations.
TL;DR: In this article, the NQR of nitrogen-14 in dichloro(dimethylnitrosamine)copper(II) was observed at low temperatures and the magnetic susceptibility measurements revealed that the compound is in an antiferro-magnetically ordered state below 6 K.
TL;DR: In this paper, a relation between the effects that the insertion of a NH + 4 impurity on a K + site has on the rigid reorientation rate of the octahedral SnCl 2−6 ion on one hand, and on the phase transition temperature on the other hand was established.
TL;DR: The frequency and variable-temperature behavior of 35Cl nuclear quadrupole resonance in three aminocyclophosphazene derivatives are reported in this paper, where the observed frequencies and multiplicity are correlated with the disposition of the substituents and the crystal structure.
TL;DR: Bromine-81 resonance frequencies in these compounds are approximately linearly related to the chlorine-35 resonance frequencies observed in the corresponding chloro-derivatives: v ( 81 Br) ≈ 8.121 v ( 35 Cl) - 29.4 as discussed by the authors.