MRSFall 2006 Meeting Nov'27Dec'1, 2006 Boston USA

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MRSFall 2006 Meeting
Nov.27-Dec.1, 2006 Boston USA
By
ARAVAMUDHAN,
Sankarampadi
Department of Chemistry

North Eastern Hill University

SHILLONG 793022 INDIA
Session
MM17.2 December 1, 2006 1100AM
Title of the Talk

Line Shapes in Magnetic
Resonance and the Average Static Magnetic Field
in the Medium The Role of Discreteness and
Continuum within the Material
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The task would be to calculate the induced field
inside the cavity scavity
Organic Molecular single crystal a specimen of
arbitrary shape
Induced field calculation by discrete summation
sinter
I.V.E Sphere
Continuum
sIVE sinter sM
Discrete
I.V.E. Cavity
Added sinter Shifts the line position
O
scavity sBulk sM
Inner Volume Element I.V.E
H
O
sintra / sM
O
O
4 point star indicates the molecule at a central
location. Structure of a typical molecule on the
right
sIVE(S)
sM
O
H
In-homogeneity can cause line shape alterations
O
Proton Site with sintra
not simply shifts only
single sharp line
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Line (position) shifts Line shape changes
NMR Line for only Intra molecular Shielding ssM
Added intermolecular sInter Contributions
causes a shift downfield or up field s
sMsInter sB (homogeneous)
Homogeneous no line shape alterations
Slightly inhomogeneous
Nearly spherical
shifted
shifted
Cylindrical
Highly inhomogeneous
Inhomogeneous Magnetization can cause line
shape alterationss sMsInter sB
(in-homogeneous)
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(1-3.cos2?) term causes ve -ve contributing
zones See drawing below
summation
Lattice
Shell by Shell
Induced field varies as R-3
Number of molecules in successive
shells increase as R2
Magnetic Field
Product of above two vary as R-1
Each moment contributes to induced field
The above distance dependences can be depicted
graphically
Dashed lines convergence limit
2 A equal spacing
Benzene Molecule Its magnetic moment
When the R becomes large, the R-1 term
contribution becomes smaller and smaller to
become insignificant
-ve zone
?M . (1-3.COS2?)/(RM)3
ve
Magnetic field direction
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First and Foremost it is to be pointed out that
trying to sum the induced field contributions in
the discrete region by taking the molecule by
molecule contributions from the neighborhood,
results in a convergence of the summed value to a
total sum, which can be termed as Intermolecular
contributions. This convergence is depicted below
in the actual single crystalline case of an
Organic molecular single crystalline system.
The summed up contributions from within Lorentz
sphere as a function of the radius of the sphere.
The sum reaches a Limiting Value at around 50Aº.
These are values reported in a M.Sc., Project
(1990) submitted to N.E.H.University. T.C. stands
for (shielding) Tensor Component .Convergence
occurred in this particular case at 50 Aº radius.