Chemistry Reference
In-Depth Information
þ
D
o
1
where D
jj¼
2
v
e
is the experimental atomization energy of
S
þ
) observed from molecular spectra (Huber and Herzberg,
1979), D
o
HF(
¼
4138 cm
1
0
:
235 E
h
the dissociation energy and
v
e
0
:
019E
h
the vibrational frequency of the vibrational ground level v
¼
0.
So, we shall use D
245E
h
.
The polarity parameter for ground state HF is then calculated to be:
jj¼
0
:
1
¼
C
2
C
1
«
1
a
p
b
¼
ð
a
p
a
h
ÞþD
l ¼
ð
2
:
125
Þ
2
jbj
We now look at the distribution of the two electrons in the
s
bonding
MO, which gives the atomic charges:
2
2
2
l
¼
1
;
¼
1
;
þ
¼
ð
:
Þ
q
F
q
H
q
F
q
H
2
2
126
2
2
l
þ
l
þ
The formal charges on the interacting atoms are:
2
¼
l
1
on F
: d
F
¼
1
q
F
1
¼jdj
ð
2
:
127
Þ
2
l
þ
2
¼
l
1
on H
: d
H
¼
1
q
H
1
¼þjdj
ð
2
:
128
Þ
2
l
þ
0, and electronic charge will be transferred fromH to F,
as expected on electronegativity grounds. As we said before, the formal
charge
For
l<
1,
d
F
<
can be independently derived from the experimentally observed
value (Muenter and Klemperer, 1970; Sileo and Cool, 1976) of the
vibrationless electric dipole moment
18
m ¼
jdj
, if we attribute the
entire value of the dipole to its heteropolar component
ð
0
:
72 ea
o
Þ
jm
H
j
(Magnasco,
2003):
jmj¼jm
H
j¼jdj
R
e
;
jdj¼
0
:
42
ð
2
:
129
Þ
so that we obtain for the polarity parameter in the case of simple p
bonding:
1
=
2
1
jdj
l ¼
¼
0
:
64
ð
2
:
130
Þ
þjdj
1
18
As usual, we assume
m >
. Calculated
Hartree-Fock values of
m
(0.756ea
o
) (Christiansen and McCullough, 1977; Sundholm et al.,
1985) corrected for correlation effects (
0 when the direction of the dipole is from -
jdj
to
þjdj
0.043ea
o
) (Werner and Meyer, 1976; Amos, 1982)
agree with the experimental result.
