Chemistry Reference
In-Depth Information
Figure 5.7
The first two permanent electric moments of some noncentrosymmetric
molecules
In the figures, a pictorial representation is given of the angular shape of the
molecular multipoles in terms of a polar diagram schematically close to that
of the corresponding atomic orbitals of quantum number l (white for the
positive lobe, dashed for the negative lobe) given in Figure 1.1 of Chapter 1.
For H
2
OandC
2
H
4
both nonvanishing quadrupole moments are given in
the figures, to outline the greater importance of
m
22
m
x
2
y
2
for H
2
O, and the
similar importance, and the different sign, of
m
20
ð¼ m
zz
Þ
and
m
22
for C
2
H
4
.
As an example of the operative use of the model, a classification of the
first few multipole interactions with their relative stability for some
selected shapes of VdW dimers is given in Figure 5.9. The interactions
are classified according to rule 2 into attractive (a) or repulsive (r), (0)
denoting the case when the interaction vanishes by symmetry. Stability is
