Determination of Nuclear Quadrupole Coupling Constants in 1:2 LiCl-Ethylaluminum Dichloride Solutions

1994 ◽  
Vol 33 (24) ◽  
pp. 5601-5603 ◽  
Author(s):  
Charles E. Keller ◽  
Bernard J. Piersma ◽  
Gilbert J. Mains ◽  
W. Robert Carper
Keyword(s):  
Coupling Constants ◽  
Quadrupole Coupling ◽  
Nuclear Quadrupole

Determination of the Sign of Nuclear Quadrupole Interaction by Laser-Radiofrequency Double-Resonance Determination of the Sign of Nuclear Quadrupole Interaction by Laser-Radiofrequency Double-Resonance

1994 ◽  
Vol 49 (1-2) ◽  
pp. 14-18
Author(s):  
Tilo Blasberg ◽  
Dieter Suter
Keyword(s):  
Quadrupole Interaction ◽  
Double Resonance ◽  
High Sensitivity ◽  
Quadrupole Coupling Constant ◽  
Nuclear Quadrupole Interaction ◽  
Coupling Constants ◽  
Quadrupole Coupling ◽  
New Type ◽  
Nuclear Quadrupole

Abstract We describe a new type of laser-radiofrequency double-resonance experiment, which allows to determine not only the absolute value but also the sign of nuclear quadrupole coupling constants. This determination of the sign, which is essential for the comparison with calculated EFG tensors, is not possible with purely magnetic experiments. The m ethod has a high resolution and, because of the optical detection, also a high sensitivity. As an example, the quadrupole coupling constant for Pr3+ :YAlO3 was measured at 4.38 K and was found to be negative.

Halogen Nuclear Quadrupole Coupling Constants in Non-axially symmetric Molecules; Ab initio Calculations, which Include Correlation, Compared with Experiment

1998 ◽  
Vol 53 (6-7) ◽  
pp. 370-382
Author(s):  
Michael H. Palmer ◽  
John A. Blair-Fish
Keyword(s):  
Ab Initio ◽  
Relativistic Effects ◽  
Close Correlation ◽  
Equilibrium Structure ◽  
Cylindrical Symmetry ◽  
Coupling Constants ◽  
Axially Symmetric ◽  
Quadrupole Coupling ◽  
Nuclear Quadrupole

Abstract Ab initio determination of the electric field gradient (EFG) tensors at halogen and other centres ena-bled determination of the nuclear quadrupole coupling constants (NQCC) for a diverse set of C2v , C3v and other symmetry molecules of general formula MH2X2 and MHX3 , where the halogen atoms (X) are Cl, Br and I, and the heavy central atoms (M) are C and Si. The study presents results at a standardised level of calculation, triple-zeta in the valence space plus polarisation functions (TZVP) for the equilib-rium geometry stage; all-electron MP2 correlation is included in all these studies. For the bromo and iodo compounds, especially the latter, it is essential to allow core polarisation, by decontraction of the p,d-functions. This is conveniently done by initial optimization of the structure with a partly contract-ed basis, followed by reestablishment of the equilibrium structure with the decontracted basis.The NQCCs, derived from the EFGs, using the 'best' values for the atomic quadruple moments Cl, Br and I, lead to good agreement with the inertial axis (IA) data obtained from microwave spectroscopy. When the data from the present study is plotted against the values derived from the IA data, obtained by whatever approximations chosen by the MW authors, we obtain a linear regression for the data (85 points) with the slope 1.0365 and intercept -0.1737, with standard errors of 0.0042 and 0.2042, respectively; these are statistically identical results irrespective of whether the data is restricted to IA or EFG principal axis (PA) data.Since as in the C3v MH3X compounds studied previously, a close correlation of the microwave spectral data with the calculations was observed using the 'best' current values for Qz , there seems no need to postulate that the values of QBr for both 79Br and 81Br are seriously in error. A scaling downwards of Qz by about 5% for Br and I increases the agreement with experiment, but the contributions of relativistic effects are unknown, and could lead to further reassessment.Of the two common assumptions used in MW spectroscopy, to convert from IA to EFG-PA data, either (a) cylindrical symmetry of the NQCC along the bond direction, or (b) coincidence of the tensor principal element with the bond axis, the latter is found to be a much more realistic approximation.

Electric-charge redistribution in the HCl subunit of hydrogen-bonded dimers B • • • HC1 from Cl nuclear quadrupole coupling: determination of the coefficient F zz of the electric-field-induced field gradient in HCl

1988 ◽  
Vol 417 (1852) ◽  
pp. 21-30 ◽  
Keyword(s):  
Electric Field ◽  
Field Gradient ◽  
Zero Point ◽  
Coupling Constants ◽  
Dimer Formation ◽  
Quadrupole Coupling ◽  
Electrical Effect ◽  
Induced Field ◽  
Nuclear Quadrupole

An interpretation is given of the chlorine nuclear quadrupole coupling constants X (Cl) for the series of dimers B • • • HCl and B • • • DCl where B = CO, C 2 H 4 , C 2 H 2 , PH 3 , H 2 S, HCN, CH 3 CN, H 2 O and NH 3 . The factors that contribute to the change in X (Cl) on dimer formation are considered in turn. First, account is taken of the effect of bond lengthening of the HCl subunit that occurs on dimer formation. Secondly, the contribution X E to the change in the coupling constant that arises from the electrical effect of B on the field gradient at the Cl nucleus in the dimer is treated at equilibrium in terms of two contributions according to the equation X E = X P + X Q = ‒ eQ {F zz F z + G zz F zz }/ h . The first term X P results from the polarization of the HCl subunit by the electric field F z due to B. The second term X Q arises from the field gradient F zz due to B but modified by the factor (l + γ zz ) = G zz , where γ zz is the usual Sternheimer antishielding factor. F zz is the corresponding factor associated with the field gradient at the Cl nucleus resulting from the polarization of the HCl subunit by the field due to B. The term X Q is directly evaluated using an available Sternheimer antishielding factor. Thirdly, allowance is made for the effect of averaging over the zero-point bending motion of the dimer. Finally, the remaining term X P has then been calculated for each member of the series B • • • HC1 and shown to be linearly dependent on F z as required by the above expression. Hence it has been possible for the first time to make an experimental determination of an F zz value of a gas-phase molecule and we report F zz = ‒116(6) x 10 10 m -1 for the HCl molecule.

Two and Three Dimensional Nuclear Quadrupole Resonance in the Investigation of Structure and Bonding

2000 ◽  
Vol 55 (1-2) ◽  
pp. 29-36 ◽  
Author(s):  
Ming-Yuan Liao ◽  
Raju Subramanian ◽  
Rachel L. Yung ◽  
Gerard S. Harbison
Keyword(s):  
Active Site ◽  
Three Dimensional ◽  
Coupling Constants ◽  
Bovine Erythrocyte ◽  
Coupling Tensor ◽  
Field Gradients ◽  
Quadrupole Coupling ◽  
Quadrupole Resonance ◽  
Nuclear Quadrupole

A variety of two dimensional two-and three-dimensional NQR experiments are reviewed, showing their application to the determination of field gradients for important sites in peptides and proteins, for assigning connected transitions of nuclei with spin ≥ 5/2, and for determining hexadecapolar coupling constants. The quadrupole coupling tensor for 63Cu in the active site of a protein, bovine erythrocyte (Cu, Zn) superoxide dismutase, has been measured and is compared with the results of ab initio calculations.

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