Showing papers on "Nuclear quadrupole resonance published in 1973"
102 citations
TL;DR: In this article, the authors measured the proton spin-lattice and rotating frame relaxations in (CH3)3CCl from 90°K to the melting point (249°K) and showed that T1ρ exhibits an inflection which is assigned to a motion of the molecule about the C-Cl bond direction.
Abstract: Proton spin‐lattice (T1) and rotating frame (T1ρ) relaxations have been measured in (CH3)3CCl from 90°K to the melting point (249°K). In Solid III (below 183°K) there is a minimum in T1 which is due to rotation of the methyl groups about an axis perpendicular to the plane containing the three protons. In this phase T1ρ exhibits an inflection which is assigned to a motion of the molecule about the C–Cl bond direction. In Solid II (from 183 to 223°K) T1 has a minimum due to the motion around the C–Cl bond direction. In the fcc Solid I the molecules are tumbling isotropically and translational diffusion is relatively fast. Chlorine‐35 nuclear quadrupole resonance (NQR) is observed in Solids III and II. The observed NQR frequency depends on temperature as predicted by the Baver theory except in the immediate vicinity of the phase transitions where the apparent torsional frequencies decrease significantly. Coefficients of self‐diffusion (D) were measured in the liquid from the melting point to the gas‐liquid c...
33 citations
TL;DR: In this paper, the phase transition in chloranil crystal has been studied by measurements of the 35Cl nuclear quadrupole resonance frequency and the spin-lattice relaxation time.
Abstract: The phase transition in chloranil crystal has been studied by measurements of the 35Cl nuclear quadrupole resonance frequency and the spin‐lattice relaxation time. The splitting of the resonance line in the low temperature phase was shown to behave as an order parameter of the phase transition. The experimental order parameter and the anomalous behavior of the transition probability (1/T1) near the transition point were interpreted satisfactorily in terms of the librational soft‐mode theory which assumes anharmonic coupling between molecular librational modes in the crystal.
30 citations
TL;DR: In this paper, the nitrogen-14 nuclear quadrupole resonance spectrum of the potassium salt of 7, 7′, 8, 8′tetracyanoquinodimethan (K-TCNQ) as found at liquid nitrogen temperature is presented.
24 citations
TL;DR: In this paper, the temperature dependence of the 35 Cl nuclear quadrupole resonance in NH 4 H(ClCH 2 CO 2 ) 2 and ND 4 D(Cl CH 2 CO2 ) 2 showed that there was a single line above 120 K and 130 K.
Abstract: Temperature dependence of the 35 Cl nuclear quadrupole resonance in NH 4 H(ClCH 2 CO 2 ) 2 and ND 4 D(ClCH 2 CO 2 ) 2 showed that there was a single line above 120 K and 130 K, respectively. Below these transition temperatures the spectrum consists of a pair of lines whose separation gradually increases at lower temperatures, being 2.17 times as large in the D salt as in the H salt. The resonance frequencies at 20.1 K were 35.1230 and 35.3680 MHz in the H salt and 35.034 and 35.566 MHz in the D salt. Infrared absorption spectra also showed splitting in the C–Cl stretching band below the transition temperature. Principal values of the electric field gradient tensors at chlorine sites were determined for the two phases of the H salt; the direction of the principal Z axes being to change asymmetrically as the transition point is traversed downwards. Two possible mechanisms, the continuous displacive transition and the order-disorder transition, were examined and shown to account equally well for the experime...
21 citations
TL;DR: In this paper, a wide range of monomeric and dimeric aluminium complexes of the type Me3AlX and (R1R2AlX)2 have been measured for stressod.
Abstract: 27 Al N.q.r. spectra have been measured for a wide range of monomeric and dimeric aluminium complexes of the type Me3AlX and (R1R2AlX)2. Measurements are also reported for But3Al, (Me2AlOMe)3, and (Me2AlSMe)n and for 69Ga in trimethylgallium. The results are interpreted in terms of the simple treatment of Townes and Dailey which is shown to account well for all the observed trends. 35Cl, 75As, 121Sb, and 123Sb n.q.r. spectra for the appropriate complexes are also reported. The potential of n.q.r. spectroscopy as a tool in structure determination is stressod.
21 citations
TL;DR: In this article, the resonance frequencies of cyclic α-chloro ethers of known configuration were analyzed and the resonance frequency of chlorine atoms in equatorial positions was shown to be 2.5 MHz higher than those of corresponding chlorine atoms at axial positions.
Abstract: 35Cl nuclear quadrupole resonance spectra of cyclic α-chloro ethers of known configuration are presented. The resonance frequencies of chlorine atoms in equatorial positions are in every case some 2.5 MHz higher than those of corresponding chlorine atoms in axial positions. Similar results are obtained for open-chain trichloromethyl ethers and the effect is sufficiently well-defined to distinguish between configurational isomers and establish their conformation. These results may be rationalised in terms of a model in which the lone-pair electrons on the oxygen atom hyperconjugate with the electrons of the CCl bond.
21 citations
TL;DR: In this paper, the α-β phase boundary for solid nitrogen has been measured with high precision between zero and 3.32 kbar using nuclear quadrupole resonance to detect the transition.
Abstract: The α-β phase boundary for solid nitrogen has been measured with high precision between zero and 3.32 kbar using nuclear quadrupole resonance to detect the transition. From an application of the Clapeyron-Clausius equation, the volume discontinuity at zero pressure is deduced to be 0.311±0.025 cm3/mole. The variation of the nuclear quadrupole resonance frequency along the phase boundary reveals that the transition occurs for a nearly constant value of the order parameter characterizing the molecular librations.
20 citations
TL;DR: In this article, a method for calculating the contribution of the zone-center (q = 0) lattice mode frequencies to the motional averaging of the nuclear quadrupole Hamiltonian in molecular crystals is described.
16 citations
16 citations
TL;DR: In this paper, a modified Townes-Dailey theory is employed to interpret the quadrupole coupling data to yield the electronic populations of the bonds between the guanidinium ions and the anions.
Abstract: Numerous ionic compounds containing the guanidinium ion have been investigated by means of nitrogen‐14 nuclear quadrupole resonance techniques. The nitrogen resonance spectrum of the amino groups of the quanidinium ions yielded, with a few exceptions, an average e 2qQ/h = 3553.6 kHz and an average asymmetry parameter η = 0.39493. The Townes‐Dailey theory is employed in interpreting the quadrupole coupling data to yield the electronic populations of the bonds. In two cases (guanidinium acetate and guanidinium carbonate) large deviations from the average quadrupole coupling parameters were observed. These deviations are interpreted, by means of a modified Townes‐Dailey theory, to indicate that hydrogen bonds are formed between the guanidinium ions and the anions.
TL;DR: In this article, a theory of the Zeeman effect of 14N nuclear quadrupole resonance with polycrystalline samples is presented and a method for the identification of lines and the measurement of asymmetry parameters is described.
Abstract: A theory of the Zeeman effect of 14N nuclear quadrupole resonance with polycrystalline samples is presented. A method for the identification of lines and the measurement of asymmetry parameters is described. The linewidth is taken into account and plays an important role. The results are general and apply for arbitrary angles between the radio‐frequency magnetic field and the Zeeman magnetic field, and for any value for the asymmetry parameter between 0.005 and 0.993. No such results exist in the literature, since the only particular case reported so far is invalidated in its quantitative aspects by an error as demonstrated in this paper. The method is shown to be useful when only one line of a pair is known, when several lines have to be identified, or when attempts are made to assign the lines in ν+, ν− pairs. The results have been experimentally verified in several cases.
TL;DR: In this article, experimental data for NQR frequency shifts as a function of temperature reveal a dominant T4 dependence at sufficiently low temperature, T ⪝ 20°K, in accord with a recent prediction.
Abstract: Analyses of experimental data for NQR frequency shifts as a function of temperature reveal a dominant T4 dependence at sufficiently low temperature, T ⪝ 20°K, in accord with a recent prediction. The results indicate the necessity of adding a Debye term to the usual Bayer expression. The coefficient of the Debye term is shown to vary with TD−5; preliminary results indicate that values of the Debye temperature TD may be obtained from low temperature NQR data.
TL;DR: In this article, the 79Br nuclear quadrupole resonance frequency and spin-lattice relaxation time in a polycrystalline sample of (NH4)2PtBr6 from 4 to 450
Abstract: Measurements of the 79Br nuclear quadrupole resonance frequency and spin–lattice relaxation time in a polycrystalline sample of (NH4)2PtBr6 from 4 to 450 K are reported. The frequency data indicate...
01 Jan 1973
TL;DR: The nitrogen atom is one of the most important atoms in organic, inorganic, and bio-chemistry as discussed by the authors and its common molecular occurrence in a variety of valence states with various types of bonding and stereochemistry has caused the nitrogen atom to be widely studied by chemical and physical techniques.
Abstract: There can be no doubt that nitrogen is one of the most important atoms in organic-, inorganic- and bio-chemistry Its common molecular occurrence in a variety of valence states with various types of bonding and stereochemistry has caused the nitrogen atom to be widely studied by chemical and physical techniques
TL;DR: The nitrogen-14 nuclear quadrupole resonance spectra of CH 3 NO 2 and of C 6 H 5 NO 2 were measured at 77°K as mentioned in this paper, and the results are: CH3 NO 2 : e 2 qQ/h = 1694.6 kHz, η = 0.4240 and C 6H 5 NO2 : e2 qQ /h = 1424.9 kHz,
01 Jan 1973
TL;DR: In this paper, the authors consider linewidths as a new piece of information about a property of the system studied, the nuclear relaxation times, which together with chemical shifts and coupling constants make up the main information content of a high-resolution NMR spectrum.
Abstract: In the present days of high resolution NMR spectroscopy, broad spectral lines are often considered as a mere manifestation of life’s everyday embarassments. One may, however, also take up the converse opinion and consider linewidths as a new piece of information about a property of the system studied, the nuclear relaxation times, which together with chemical shifts and coupling constants† make up the main information content of a high resolution NMR spectrum. Nuclear relaxation times are characteristic time constants representing the rate of change of the longitudinal (longitudinal or spin-lattice relaxation time T 1) or of the transverse (transverse or spin-spin relaxation time T 2) components of the macrosopic nuclear magnetization. They are determined by the interactions existing within the spin-system and between the spins and the lattice.
TL;DR: In this paper, a diatomic linear-chain model was proposed to explain the dependence of the nuclear-quadrupole-resonance frequencies on the librational and vibrational coordinates at the low frequencies of acoustic phonons.
Abstract: Nuclear-quadrupole-resonance frequencies are shown to have a ${T}^{4}$ dependence which becomes dominant at sufficiently low temperatures; the mechanism is discussed using a diatomic linear-chain model. The uniform-translational character of the acoustic phonons is shown to produce a ${T}^{4}$-dependent Doppler shift which is too small to account for the experimental results. The nonuniform $q$-dependent character of the acoustic branch is shown to induce modulations of the librational and vibrational coordinates at the low frequencies of the acoustic phonons. A Debye term is added to the familiar Bayer expression; both terms are shown to be produced by the modulation of the same coordinates, except that they occur at different frequencies.
TL;DR: In this article, the trichloromethyl group of benzotrichlorides and derivatives of heterocyclic molecules were compared with the same group attached to other planar conjugated radicals.
Abstract: 35Cl nuclear quadrupole resonance frequencies are reported of the chlorine atoms in the trichloromethyl group of benzotrichlorides and trichloromethyl derivatives of heterocyclic molecules. They are compared with previously reported results for the same group attached to other planar conjugated radicals. In such compounds the three chlorine atoms cannot be equivalent and all the results are discussed from the point of view of possible orientation-dependant hyperconjugation between the CCl bonds and the conjugated moiety, particularly with reference to the marked effects observed in trichloromethyl ethers reported in part I of this series. In the benzo-trichloride and indeed most of the compounds discussed such effects are small.
TL;DR: The nuclear quadrupole resonance of nitrogen-14 in potassium tetracyanomercurate (II) was observed in a temperature range of 4.2-400 K as discussed by the authors.
TL;DR: In this article, a librational soft mode theory based on an anharmonic coupling between molecular or ionic modes in the ionic crystal PCl4+·PCl6− was presented.
Abstract: Chlorine-35 nuclear quadrupole resonance frequencies in the ionic crystal PCl4+·PCl6− were redetermined. Ten resonance lines were found and their temperature dependences were measured below the second order phase transition point at 102 K. The splitting Δvi in the resonance lines in the low temperature phase showed a similar temperature dependence as the order parameter. This was accounted for by a librational soft mode theory based on an anharmonic coupling between molecular or ionic librational modes in the crystal.
TL;DR: In this paper, a correlation between the molecular core binding energy of chlorine in square-planar platinum chlorides and their 35Cl n.q.r. frequencies was established.
Abstract: A correlation has been established between the molecular core binding energy of chlorine in square-planar platinum chlorides and their 35Cl n.q.r. frequencies. This is used, together with measured core binding energies, to discuss structure and bonding in Zeise's salt and its analogues.
TL;DR: In this paper, the anion sensitivity to the cation is not readily predictable on the basis of the size alone, and it is concluded that the sensitivity of the TeCl62− ion to the ion cation can not be reliably predicted.
Abstract: N.q.r. frequencies of 14 salts of SnCl62–, TeCl62–, and PbCl62– have been recorded in an effort to observe possible differences in anion distortion which could result from the ‘inert’ pair electrons of TeIV. There is no evidence of stereochemical activity of the TeIV‘inert’ pair as might be indicated by an increase in the number of chlorine resonance frequencies and/or anomalous changes in bond ionicity in any of the compounds studied. PbCl62– appears to be more sensitive to the cation than SnCl62– but the TeCl62– ion is less sensitive. It is concluded that anion sensitivity to the cation is not readily predictable on the basis of the size alone.
TL;DR: The nuclear quadrupole resonance of halogens in X3SnMn(CO)5, where X stands for chlorine, bromine, and iodine, was observed between liquid nitrogen and room temperatures.
TL;DR: In this article, the quadrupole moment of the 535 keV 3 2 − state of 133La was derived from a time-differential perturbed angular correlation measurement in an environment of La metal.
TL;DR: The complete nitrogen 14 nuclear quadrupole resonance spectra of six nitrosamines at 77°K have been determined with cw and pulsed techniques as mentioned in this paper, and the N−N bond was found to be slightly polarized toward the amino nitrogen atom, the charge unbalance of this bond amounts to about 0.08 electrons.
Abstract: The complete nitrogen‐14 nuclear quadrupole resonance spectra of six nitrosamines at 77°K have been determined with cw and pulsed techniques. Absorption lines belonging to the amino nitrogen atom lie at rather low frequencies and are virtually undetectable with cw techniques. The low frequencies of the amino lines indicates a considerable loss of π charge to the oxygen atom. As a result of this charge transfer, the polarity of the N=O bond is smaller than the polarity of a N–OH bond. The N–N bond was found to be slightly polarized toward the amino nitrogen atom, the charge unbalance of this bond amounts to about 0.08 electrons.
TL;DR: In this article, the data on 137 Ba quadrupole couplings in barium halide dihydrates is presented, and the isomorphism of barium bromide and iodide diohydrates is discussed.