The topology of the valence shell and the electric field gradient at the nitrogen nucleus in aziridines

1996 ◽  
Vol 74 (6) ◽  
pp. 1116-1120
Author(s):  
Félix Rosillo ◽  
Yosslen Aray ◽  
Jesús Rodríguez ◽  
Juan Murgich
Keyword(s):  
Electric Field ◽  
Electric Field Gradient ◽  
Charge Density ◽  
Field Gradient ◽  
Valence Shell ◽  
Nitrogen Nucleus ◽  
Principal Axes ◽  
Molecular Charge ◽  
Charge Concentration ◽  
C And N

The ab initio molecular charge density ρ(r) of substituted aziridines was calculated at the MP2 level for R = -H, -CH3, -CF3, -Cl, -NO2, -CN, -OH, -NO, and -F. The use of the topology of the Laplacian of ρ(r) allowed the analysis of the electric field gradient (EFG) at the nitrogen nucleus directly in terms of its valence shell charge concentration. The EFG changed sign and the orientation of its y- and z-axes with respect to aziridine when R = -Cl, -NO2, -CN, -OH, -NO, and -F. The changes in the EFG in these aziridines upon substitution were correlated with those calculated in the valence charge concentrations along the direction of the N—R bond. The sign of the qzz component and the orientation of the principal axes of the EFG tensor were found to be determined by the relative value of the contributions from the charge concentrations at the points in the valence shell along the N—C and N—R bond directions. Key words: molecular charge distribution, aziridines, Laplacian of the charge density, electric field gradient.

NUCLEAR ELECTRIC QUADRUPOLE INTERACTION IN SINGLE CRYSTALS

1952 ◽  
Vol 30 (3) ◽  
pp. 270-289 ◽  
Author(s):  
G. M. Volkoff ◽  
H. E. Petch ◽  
D. W. L. Smellie
Keyword(s):  
Electric Field ◽  
Electric Field Gradient ◽  
Field Gradient ◽  
Electric Quadrupole ◽  
Quadrupole Coupling Constant ◽  
Coupling Constant ◽  
Gradient Tensor ◽  
Absolute Value ◽  
Principal Axes ◽  
Quadrupole Coupling

Pound's theory of the dependence of electric quadrupole splitting of nuclear magnetic resonance absorption lines in a single crystal on the orientation of the crystal in an external magnetic field is extended to cover the case of a crystal with nonaxially symmetric electric field gradient at the site of the nuclei being investigated. It is shown that an experimental study of the angular dependence of this splitting for three independent rotations of the crystal about any three mutually perpendicular axes will yield complete information about the orientation of the principal axes and the degree of axial asymmetry of the electric field gradient tensor at the site of the nuclei, and also will give the absolute value of the quadrupole coupling constant for those nuclei.The authors' experiments on the splitting of the Li7 absorption lines in a single crystal of LiAl(SiO3)2 (spodumene) are described and are used to illustrate the theory. The absolute value of the quadrupole coupling constant for the Li7 nuclei in spodumene is found to be [Formula: see text]. per sec. The axial asymmetry parameter of the field gradient tensor at the site of the Li nuclei is found to be η≡(ϕxx−ϕvv)ϕzz=0.79 ± 0.01. One of the principal axes of this tensor (the y axis corresponding to the eigenvalue of intermediate magnitude) is experimentally found to coincide with the b crystallographic axis of monoclinic spodumene as required by the known symmetry of the crystal. The other two principal axes are in the ac plane, the z axis (corresponding to the eigenvalue ϕzz of greatest magnitude) lying between the a and c axes at an angle of 48° ± 2° with the c axis.

Hyperfine Interaction Induced K-type Doubling in the mmw Spectrum of HS33SH

1995 ◽  
Vol 50 (12) ◽  
pp. 1191-1198 ◽  
Author(s):  
Axel H. Saleck ◽  
Gisbert Winnewisser
Keyword(s):  
Electric Field ◽  
Electric Field Gradient ◽  
Field Gradient ◽  
Hyperfine Interactions ◽  
Electric Quadrupole ◽  
Rotational Spectrum ◽  
Hyperfine Parameters ◽  
Gradient Tensor ◽  
Principal Axes ◽  
Good Agreement

Abstract The rotational spectrum of the disulfane isotopomer HS33SH has been recorded and assigned between 70 and 300 GHz. In the analysis, rotational constants and 33S hyperfine parameters are derived, the latter accounting for nuclear electric quadrupole as well as nuclear spin -rotation hyperfine interactions. The quadrupole constants are in qualitative agreement with a published ab-initio calculation. The electric field gradient principal axes are considerably rotated against the principal inertial axes, giving rise to off-diagonal elements in the electric field gradient tensor. In combination with the very small inertial asymmetry of the molecule, this causes the A'-doubling in the lowest rotational levels to be dominated by the hyperfine structure rather than the inertial asymmetry contributions. By diagonalization of the quadrupole tensor, an estimate for the dihedral angle (η≈94°) can be obtained, in good agreement with a previous value.

Criteria for assessing theoretically derived electric field gradient tensor components

1977 ◽  
Vol 30 (9) ◽  
pp. 1869 ◽  
Author(s):  
M Sheps ◽  
S Hacobian
Keyword(s):  
Electric Field ◽  
Electric Field Gradient ◽  
Field Gradient ◽  
Approximation Schemes ◽  
Hydrazoic Acid ◽  
Gradient Tensor ◽  
Principal Axes ◽  
Set Up ◽  
Lcao Mo

It is possible to set up an electric field gradient criteria scheme as an aid in assessing the quality of theoretically derived electric field gradient (EFG) tensor components characterized by a non-zero asymmetry parameter. The analysis draws attention to the importance of checking that the theoretically predicted coordinate axes assignments of the principal axes system (PAS) for the EFG tensor components respectively agree with the assignments of the experimental PAS. An application of the PAS-assignment-criterion shows that some well known LCAO MO based EFG approximation schemes when tested on the hydrazoic acid molecule possess a serious limitation, as evidenced by their failure to obey this criterion.

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