共查询到20条相似文献,搜索用时 31 毫秒
1.
Robert W. Schurko Roderick E. Wasylishen Andrew D. Phillips 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,133(2):388-394
Solid-state27Al NMR spectra have been obtained for a crystalline 1:1 complex of AlCl3and OPCl3. Aluminum chloride phosphoryl chloride, AlCl3· OPCl3(1), is unusual in that the Al–O–P bond angle is close to 180°. From analysis of the27Al MAS NMR spectra, it was determined that the27Al nuclear quadrupole coupling constant is 6.0(1) MHz, the asymmetry in the electric field gradient (efg) tensor is 0.15(2), and the isotropic chemical shift, δiso(27Al), is 88(1) ppm. Solid-state27Al NMR of a stationary sample reveals a line shape affected by a combination of anisotropic chemical shielding and second-order quadrupolar interactions. Analysis of this spectrum yields a chemical shift anisotropy of 60(1) ppm and orientations of the chemical shift and electric field gradient tensors in the molecular frame. Experimental results are compared with those calculated usingab initioHartree–Fock and density functional theory. 相似文献
2.
Spinning Sidebands in Slow-Magic-Angle-Spinning NMR Spectra Arising from TightlyJ-Coupled Spin Pairs
Gang Wu Boqin Sun Roderick E. Wasylishen Robert G. Griffin 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1997,124(2):366-371
Complex spinning sidebands are observed in magic-angle-spinning (MAS) NMR spectra arising from isolated tightlyJ-coupled spin pairs under slow spinning conditions. Such spinning sidebands are sensitive to the magnitude and relative orientation of the chemical-shift tensors, the dipolar-coupling tensor, and the sign of the indirect spin–spin (J) coupling. We show that it is possible to extract information concerning such NMR parameters from an analysis of the observed spinning sidebands. As an example, numerical simulations are carried out to reproduce observed31P MAS NMR spectra of a phosphole tetramer (1) ando-bis(diphenylphosphino)benzene (2), so that invaluable information concerning the orientations of the phosphorus chemical-shift tensors and the sign ofJ(31P,31P) can be deduced. Simulations are carried out by numerically evaluating the spin-density matrix of the spin system. 相似文献
3.
Karim Elbayed Pierre Kempgens Jésus Raya Pierre Granger Jacky Rosé 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,130(2):209-216
The formalism for calculating the lineshape of a spin 1/2J-coupled to a high-spin nucleus undergoing quadrupolar and chemical shift anisotropy (CSA) relaxations is derived in the case where the tensors of both interactions are noncoincident and nonaxial. The expressions show that the CSA–quadrupolar interference term which is responsible for the asymmetry of lines involves a term depending on tensorial parameters. The effect of this term on the lineshapes is discussed with respect to three cases, namely coincident–axially symmetric, noncoincident–axially symmetric, and general noncoincident quadrupolar and CSA tensors. These cases are considered in the analysis of the lineshape of the1H-decoupled spectra of the31P nucleusJ-coupled to the59Co nucleus encountered in the tetrahedral cluster HFeCo3(CO)11PPh2H. 相似文献
4.
MATTHIAS BECHMANN STEPHAN DUSOLD HANS FÖRSTER ULRICH HAEBERLEN TADEUSZ LIS ANGELIKA SEBALD 《Molecular physics》2013,111(9):605-617
A 31P and 13C NMR study of powder and single crystal samples of two phosphoenolpyruvate (PEP) compounds, the tris-ammonium salt monohydrate (NH4)3(PEP)·H2O (1), and the mono-ammonium-salt (NH4)(H2PEP) (2) is presented. The P chemical shielding tensors in 1 are measured by 31P single crystal NMR on four minuscule samples and assigned without ambiguity by exploiting the orientation-dependent 31P-31p dipolar splittings of the resonance lines. The orientation of the 31P chemical shielding tensor is discussed in terms of the C2v — and C3-type distortions of the phosphate PO4-coordination sphere. From 13C MAS NMR experiments with 31P rotary resonance recoupling on polycrystalline powder samples the orientations of the 31P chemical shielding tensors in 1 and 2 are obtained, for 1 in very good agreement with the 31P single crystal NMR results. Only some of the orientational parameters of the three 13C chemical shielding tensors in the PEP moiety of 1 could be derived from 13C MAS NMR experiments with 31P rotary resonance recoupling. 相似文献
5.
《Solid state nuclear magnetic resonance》2010,37(4):182-191
Using 31P solid-state NMR spectroscopy, anisotropy in the indirect 199Hg-31P spin–spin coupling tensor (ΔJ) for powdered [HgPCy3(OAc)2]2 (1) has been measured as 4700±300 Hz. Zeroth-order regular approximation (ZORA) density functional theory (DFT) calculations, including scalar and spin-orbit relativistic effects, performed on 1 and a series of other related compounds show that ΔJ(199Hg, 31P) arises entirely from the ZORA Fermi-contact–spin-dipolar cross term. The calculations validate assumptions made in the spectral analysis of 1 and in previous determinations of ΔJ in powder samples, namely that J is axially symmetric and shares its principal axis system with the direct dipolar coupling tensor (D). Agreement between experiment and theory for various 199Hg, 31P spin–spin coupling anisotropies is reasonable; however, experimental values of 1J(199Hg, 31P)iso are significantly underestimated by the calculations. The most important improvements in the agreement were obtained as a result of including more of the crystal lattice in the model used for the calculations, e.g., a change of 43% was noted for 1J(199Hg, 31P)iso in [HgPPh3(NO3)2]2 depending on whether the two or three nearest nitrate ions are included in the model. Finally, we have written a computer program to simulate the effects of non-axial symmetry in J and of non-coincidence of the J and D on powder NMR spectra. Simulations clearly show that both of these effects have a pronounced impact on the 31P NMR spectrum of 199Hg–31P spin pairs, suggesting that the effects should be observable experimentally if a suitable compound can be identified. 相似文献
6.
Najate Bensari-zizi Claude Alamichel 《International Journal of Infrared and Millimeter Waves》1989,10(1):137-151
About 2500 lines of CH3
35Cl have been assigned. The strong xy Coriolis resonance between thev
2 andv
5 modes is quite visible between thev
4+v
4
±1
perpendicular band, centered around 4383 cm–1, and thev
4
±1
+v
5
±1
perpendicular component, centered around 4475 cm–1, with a crossing of upper energy levels allowing the observation of lines which are normally forbidden. Although not yet observed with certainty, because of the great density of lines of the spectrum, thev
4
1
+v
5
±1
parallel component is nevertheless detectable by its effects onv
2+v
4
±1
which is linked by Coriolis resonance to both components ofv
4+v
5. Moreover the spectrum is much complicated by many other resonances with weak bands which occur at level crossings: it is the case ofv
2+3v
6
±1
, connected tov
2+v
4
±1
by the well known Darling Dennison resonance which couplesv
4
±1
and 3v
6
±1
, and also ofv
5
±1
+3v
6
±1
connected tov
4
±1
+v
5
±1
by the same resonance; but this last case is complicated by an anharmonic resonance betweenv
5
±1
+3v
6
±1
and 2v
3+3v
6
1
. Two more perturbations occur on the K=–1 side ofv
2+v
4: a weak Coriolis resonance gives rise to one subband ofv
1+v
2 at a level crossing withv
2+v
4, and thev
1+v
5 band (linked of course tov
1+v
2 by the Coriolis resonance between thev
2 andv
5 modes) is quite visible and perturbs several subbands ofv
2+v
4 of high values of K through an anharmonic resonance. Moreover, the complex (3v
5
±1
,v+2v
5
0
, 2v
2+v
5
±1
, 3v
2,v
2+2v
5
±2
, 3v
5
±3
) system of Coriolis-connected bands is linked to the bands studied in the present work by two Fermi resonances: one betweenv
2+2v
5
0
andv
1+v
2, and the other one betweenv
1+v
5 and 3v
5
±1
, whose several subbands have been observed on the low part of the spectrum. The values of all the band centres and of the different coupling constants have been estimated, but all these interactions make the line assignments and the interpretation of the spectrum very difficult. 相似文献
7.
Mössbauer effect measurements have been made using57Fe in FeSb2O4. At liquid helium temperature a combined electric quadrupole and magnetic hyperfine interaction is observed withH
eff=185±2 kOe, 1/2e
2
qQ=2.94±0.09 mm/sec and =0.37±0.09. The direction ofH
eff is perpendicular to thec axis of the crystal and at 33° to the <110> direction. Thec axis is determined to be the direction of the intermediate principal EFG tensor axis. Calculations are made using a molecular field term in the Hamiltonian for the Fe2+ orbitals. The results of these calculations are used to explain the observed values of 1/2e
2
qQ and and permit a determination of the ordring of the T2g orbitals among the T2g energy levels. 相似文献
8.
《Journal of Magnetic Resonance, Series A》1993,101(2):157-161
Phosphorus-31CP-MAS spectra of Cd(NO3)2(PPh3)2 have been obtained as a function of spinning frequency. Although the two 31P nuclei are crystallographically equivalent and have the same isotropic chemical shifts in the solid state, they exhibit spinning-rate-dependent MAS spectra which have been analyzed to obtain the value of 2J(P, P). At high spinning rates, the spectra are analogous to "A2" spectra in isotropic solutions, while at slower spinning rates, the spectra are more characteristic of strongly coupled "AB" solution spectra. The AB spectra are unusual in that δA = δB and J(A, B) is given by the splitting between the alternate peaks in the four-peak multiplet as opposed to the splitting between the outer and adjacent inner lines. This assignment was confirmed by a 2D CP-MAS J-resolved experiment. The unusual spinning-rate-dependent MAS lineshapes result from recoupling of the J interaction between the two crystallographically equivalent nuclei via anisotropic interactions, i.e., weak homonuclear dipolar coupling and differences in the orientation dependence of the chemical-shift tensors. Such spinning-rate-dependent MAS lineshapes are predicted to be a more frequent observation at higher applied magnetic fields. 相似文献
9.
I. Sack S. Macholl F. Wehrmann J. Albrecht H. H. Limbach F. Filiaux M. H. Baron G. Buntkowsky 《Applied magnetic resonance》1999,17(2-3):413-431
The solid-state1H MAS (magic-angle spinning),2H static,15N CP (cross polarization)-MAS and15N-1H dipolar CSA (chemical shielding anisotropy) NMR (nuclear magnetic resonance) spectra of two different modifications of Cα-deuteratedl5N-polyglycine, namely PG I and PG II (-CO-CD2-l5NH-)n are measured. The data from these spectra are compared to previous NMR, infrared, Raman and inelastic neutron scattering work. The deuteration of Cα eliminates the largest intramolecular1H-1H dipolar coupling. The effect of the remaining (N)H-(N)H interaction (~5 kHz) is not negligible compared to the15N-1H coupling (about 10 kHz). Its effect on the dipolar CSA spectra, described as a two-spin system, is analyzed analytically and numerically and it is shown that those parts of the powder spectrum, which correspond to orientations with a strong dipolar15N-1H interaction, can be described as an effective two-spin system, permitting the measurement of the strength of the15N-1H dipolar interaction and the orientation of the dipolar vector with respect to the15N CSA frame. While in the PG II system the15N CSA tensor is collinear with the amide plane, in the PG I system the CSA tensor is tilted ca. 16° with respect to the (δ11δ22) CSA plane. 相似文献
10.
Hsien-Ming Kao Clare P Grey 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,133(2):313-323
Coherence transfer from quadrupolar27Al (I=
) nuclei to31P (I=
) via INEPT experiments is investigated.27Al →31P INEPT experiments on a (CH3)3P–AlCl3complex in zeolite NaX are performed, and the results demonstrate that the31P INEPT signals strongly depend on whether or not the27Al pulses are applied synchronously with the rotor period, and on the length of the27Al pulses. A density-matrix calculation involving the use of the spin operators for spin
and
nuclei has been performed to help understand the evolution behavior of the density matrix under the influence of the quadrupolar interaction, the dipolar andJ-couplings, and the pulse lengths applied to the quadrupolar nuclei. The theoretical predictions obtained from these calculations are consistent with the INEPT experimental observations. 相似文献
11.
12.
Rotem Vardi Marcelino Bernardo Hans Thomann Karl G. Strohmaier David E.W. Vaughan Daniella Goldfarb 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1997,126(2):229-241
X-band (∼9.3 GHz) pulsed ENDOR measurements were carried out on57Fe-substituted sodalite (FeSOD) which contains only one type of Fe(III) (S=) located at a framework site. The ENDOR spectrum recorded atg= 2 shows three doublets corresponding to the sixMSmanifolds. The assignment of these signals was confirmed by hyperfine-selective and triple ENDOR experiments. The components of each of the doublets had different intensities, reflecting the different populations of the EPR energy levels at the measurement temperature, 1.8 K. ENDOR spectra were recorded at magnetic fields within the EPR powder pattern, and the field dependence observed showed an anisotropic behavior, unexpected from the isotropic character of the57Fe(III) hyperfine coupling. This dependence was attributed to the high-order effects of the zero-field splitting (ZFS) interaction on the ENDOR frequencies. Three different theoretical approaches were used to account for the dependence of the ENDOR spectrum on the ZFS interaction. The first involves the exact diagonalization of the total spin Hamiltonian, the second uses third-order perturbation approximations, and the third employs an effective nuclear Hamiltonian for each of theMSmanifolds. The simulations showed that the ENDOR signals of theMS= ±5/2 (ν±5/2) manifold are the least sensitive to the magnitude of the ZFS parameterDand are therefore the most appropriate for the determination ofaiso. It is shown that at X band andaisovalues of about 30 MHz, the perturbation approach is valid up toDvalues of 500 MHz if all three doublets are concerned. However, if only the ν±5/2doublet is considered, then this approach is valid forD< 1000 MHz. The third approach was found inappropriate foraisovalues of ∼30 MHz. Using the method of exact diagonalization together with orientation selectivity, the trends observed in the experimental spectra could be reproduced. The ENDOR spectra of the57Fe-substituted zeolites ZSM5, L, and mazzite showed broad and ill-defined peaks since the ZFS of Fe(III) in these zeolites is significantly larger than that of FeSOD. Because this broadening is a high-order effect, it can be significantly reduced at higher spectrometer frequencies. 相似文献
13.
J. Eberz U. Dinger T. Horiguchi G. Huber H. Lochmann R. Menges R. Kirchner O. Klepper T. Kühl D. Marx E. Roeckl D. Schardt G. Ulm 《Zeitschrift für Physik A Hadrons and Nuclei》1986,323(1):119-123
The hyperfine structure and isotope shift of108gIn and108mIn have been investigated by means of collinear fast-beam laser spectroscopy in the resonance line atλ=451 nm. The indium isotopes were prepared at the GSI on-line mass separator following a fusion evaporation reaction. For the first time, a FEBIAD ion source with bunched release of indium was used. Magnetic dipole moments, electric quadrupole moments and isotope shifts were determined. The present results lead us to assign the spinI=2 to the108In (T 1/2=40 min) state. Spins and moments are discussed in the framework of thejj-coupling model. 相似文献
14.
-rays emitted after thermal neutron capture in122Te have been investigated for the first time. Energies and intensities of 80 transitions assigned to123Te have been determined. Fortyeight of these transitions have been placed in the123Te level scheme among 27 excited levels. Two new levels of 1808·8 and 2092·3 keV,J=(1/2, 3/2), have been observed. The neutron binding energy has been found to be 6929·1±0·5 keV. The role of direct capture mechanism has been examined. 相似文献
15.
Matthias Baur Gerd Gemmecker Horst Kessler 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,132(2):191-196
Two new pulse sequences are presented for the recording of 2D13C-HSQC and 3D13C-NOESY-HSQC experiments, containing two consecutive carbon evolution periods. The two periods are separated by az-filter which creates a clean CxHz-quantum state for evolution in the second period. Each period is incremented (in anon-constant-time fashion) only to the extent that the defocusing of carbon inphase magnetization throughJ-coupling with neighboring carbons remains insignificant. Therefore,13C homonuclearJ-couplings are rendered ineffective, reducing the loss of signal and peak splitting commonly associated with long13C evolution times. The two periods are incremented according to a special acquisition protocol employing a13C–13C gradient echo to yield a data set analogous to one obtained by evolution over the added duration of both periods. The spectra recorded with the new technique on uniformly13C-labeled proteins at twice the evolution time of the standard13C-HSQC experiment display a nearly twofold enhancement of resolution in the carbon domain, while maintaining a good sensitivity even in the case of large proteins. Applied to the IIAManprotein ofE. coli(31 kDa), the13C-HSQC experiment recorded with a carbon evolution time of 2 × 8 ms showed a 36% decrease in linewidths compared to the standard13C-HSQC experiment, and theS/Nratio of representative cross-peaks was reduced to 40%. This reduction reflects mostly the typical loss of intensity observed when recording with an increased resolution. The13C-NOESY-HSQC experiment derived from the13C-HSQC experiment yielded additional NOE restraints between resonances which previously had been unresolved. 相似文献
16.
Results of measurement between 746 and 1231 C of the diffusion coefficient Fe-59 in the Fe-17·6 at.% V alloy, together with Mirani's et al., Lai-Borg's and Hettich's et al. data analysis, are presented. All the data show a marked ferromagnetic effect, i.e. the lnD(T) values measured at the temperaturesT< are distinctly lower than those extrapolated by the linear Arrhenius plot from the paramagnetic range. The results are interpreted in terms of the Heisenberg model, Kirkwood's and Girifalco's statistical theories. The computer fit of an analytical form, derived for the excess activation enthalpyH(T), to experimental data enabled us to calculate the values of the exchange integralJ
0 and the paramagnetic temperatureT
p. The corresponding values for the Fe-17·6% V alloy are:J
0=(315±11)k,k is the Boltzmann constant, andT
p=(1223±±18) K. The activation enthalpy of Fe self-diffusion in a completely ordered ferromagnetic Fe-17·6% V matrix is higher by the value ofH(0)=(55·2±1·9)kJ/mol than the value 236·35 kJ/mol corresponding to a fully paramagnetic state. Applying a three paramagnetic fit to Mirani's, Lai-Borg's and Hettichs data, we have found that the ratio of the vacancy migration enthalpy and of the formation enthalpy in -Fe, in Fe-17·6% and Fe-7·64% Si, may be expressed by the valueH
M/H
F=1·62 ± 0·18. A comparison ofJ
0(-Fe) toJ
0(17·6 %V) and toJ
0(7·64% Si) shows that the magnetic dilution caused by 17·6% of vanadium is negligible withJ
0(17·6% V)/ /J
0(-Fe)=0·999. The dilution brought about by silicium is by about 1·24 times higher, and the ratioJ
0(7·64% Si)/J
0(-Fe)=0·86. The paramagnetic temperatures in the materials under study are given by the relationT
P=(gQ + 137) K, being the respective Curie-temperature. The present analysis makes it possible to calculate the Fe diffusion characteristicsD
0f aH
f in a fully ordered magnetic matrix. 相似文献
17.
S. F. Sagnowski Z. Sulek M. Stachura J. Ogar 《Zeitschrift für Physik B Condensed Matter》1982,46(2):123-129
Single crystals of sodium nitrate, sodium chlorate and sodium bromate were investigated by continuous wave and Fourier transform pulse techniques. The sodium shielding tensors for studied compounds were found from the shift of the central line of23Na triplet, which was measured as a function of the crystal orientation. The shielding appears isotropic in NaNO3 and anisotropic in chlorate and bromate salts; the anisotropies are 0±2, 12±1 and 17±1 ppm respectively. It is suggested that lattice forces lowering the local symmetry at the sodium site are responsible for the observed effects of shielding anisotropy. 相似文献
18.
The excitation functions of the29Si(d, p)30Si reaction in the deuteron energy range of 1·1–2·1 MeV have been measured in steps of 9.3 keV at angles 40°, 60°, 90°, 100°, 110°, 130° and 150° for the following groups of protons: po (g.s. of the30Si nucleus), p1 (2·23 MeV), p2 (3·51 MeV), p3,4 (3·77 and 3·79 MeV), p5,6 (4·81 and 4·83 MeV), p10 (5·48 MeV) and pn (5.61 MeV). Within the framework of Ericson's theory of statistical fluctuations the autocorrelations, cross-angle correlations and cross-group correlations have been calculated and the mean coherence width of the31P compound nucleus has been deduced to be 27 keV.The authors would like to express their thanks to K. Putz for the efficient performance of the electronical equipment and to the staff of the Van de Graaff laboratory for operating the accelerator. 相似文献
19.
《Solid state nuclear magnetic resonance》2007,31(3-4):162-170
We report the first experimental determination of the carboxylate oxygen electric-field-gradient (EFG) and chemical shielding (CS) tensors in polycrystalline γ-glycine. Analysis of magic-angle spinning (MAS) and stationary 17O NMR spectra of [17O]-γ-glycine obtained at 9.4, 14.1, 16.4, and 18.8 T yields the magnitudes of the 17O EFG and CS tensors and the relative orientations between the two tensors. Extensive quantum chemical calculations at both the restricted Hartree–Fock and density functional levels have been performed to present the absolute tensor orientations in term of the molecular frame. We have demonstrated that 17O NMR tensor information could be unambiguously derived by the multiple field analyses of stationary 17O NMR spectra. 相似文献
20.
The experimentalN andO shell conversion coefficients of highly hinderedE1 transitions were found to be anomalous. The discrepancies as well as those for theL andM shells were removed by using the following values of the nuclear current parameter: 9·2±0·1 for the 6·21 keV transition in181Ta, 8·5±0·5 or –7·5±0·5 for the 84·20 keV transition in231Pa and 1·9±0·2 for the 26·38 keV one in237Np. 相似文献