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by the physical process of electronegativity equalization. Let the electronegativities
of the atom A and B in the molecule AB are χ/
A
and χ/
B
respectively. The principle of
electronegativity equalization provides,
χ
AB
= χ/
A
= χ/
B
(41)
Now, on the basis of SBC model, Ray et al. [17] derived the internuclear bond
distances of hetero nuclear diatomics using the concept of electronegativity equaliza-
tion and the zero order approximation of Pasternak [21], that is, r
A
= r
1
and r
B
= r
2
. We
reproduce below the process of evaluation of inter nuclear equilibrium bond distance
of Ray et al. [17].
R
AB
= (r
A
+ r
B
) - {(r
A
r
B
(χ
1/2
A
- χ
1/2
B
)
2
}/(χ
A
r
A
+ χ
B
r
B
)
(42)
where r
A
and r
B
are the covalent radii of the atom A and B respectively.
In a recent work, Ghosh and Islam [39-43] have modifi ed the expression for com-
puting the inter nuclear bond distances in terms of electronegativity and size data of
atoms by substituting the covalent radii by most probable radii or absolute radii of
atoms in the above equation
.
The modifi ed expression of R
AB
is:
R
AB
= (r
A
/
+r
B
/
) - {(r
A
/
r
B
/
(χ
1/2
A
- χ
1/2
B
)
2
}/(χ
A
r
A
/
+ χ
B
r
B
/
)
(43)
where r
A
/
and r
B
/
are the most probable radii or absolute radii of the atoms A and B
respectively.
ATOMIC POLAR TENSOR
Kim [44] extended the SBC model to evaluate the Atomic polar tensor. He showed that
electronegativity and the electronegativity equalization can be used as an important
tool for the determination of Atomic Polar Tensor in case of diatomic molecule.
Kim [44] evaluated the dipole charge as:
q = { r
1
r
2
/CR
AB
}(χ
B
- χ
A
)
(44)
The centroid of positive charge r, relative to the point defi ning the centroid of
negative charge is given as:
r = {r
2
Z
B
- r
1
Z
A
- (r
1
+ r
2
) q}/(Z
A
+ Z
B
)
(45)
Kim [44] defi ned the dipole moment, μ, as:
μ = (Z
A
+ Z
B
)r = - (r
1
+ r
2
) q + (r
1
Z
B
- r
2
Z
A
)
= - R
AB
q + (r
2
Z
B
- r
1
Z
A
)
= - 1/C [(r
A
r
B
χ
A
χ
B
)/(r
A
χ
A
+
r
B
χ
B
)
2
][R
2
AB
(χ
B
- χ
A
)]
(46)
For AB type diatomic molecule, where A atom is located at the origin and B atom
in positive Cartesian direction and χ
B
< χ
A
the atomic polar tensors (P
x
's) for atoms. A
and B was given as:
P
x
B
= - P
x
A
= (∂μ/∂R)
e
(47)
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