Chemistry Reference
In-Depth Information
-3
Δ
Ε
/10
Ε
h
1
Σ
+
,
312.5
MO
1.4
0
R
/
a
0
HL
Chemical Bond
Δ
Ε
-6
Δ
Ε
/10
Ε
h
3
Σ
+
,
R
/
a
0
8
VdW Bond
0
R
Scattering State
Figure 9.2 MO and HL potential energy curves for
1
S
g
ground state (top) and
3
S
u
excited state (bottom) of the H
2
molecule
energy. This large correlation error can be removed through CI of the
ground-state
2
2
s
g
configuration with the doubly excited configuration
s
u
,
where both electrons occupy the
s
u
antibonding MO, leaving
s
g
empty.
The interconfigurational wavefunction
1
g
Þ¼
N
½Yðs
2
g
1
g
ÞþlYðs
2
u
1
g
Yð
MO-CI
;
S
;
S
;
S
Þ
ð
9
:
27
Þ
with the variationally optimized mixing parameter
l
0
:
13 at
R
e
¼
1
4a
0
, now correctly describes dissociation of the molecule into
two neutral H atoms in their ground state.
:
9.2.2 Heitler-London Theory
Heitler and London (1927) proposed for H
2
the two-configuration
wavefunction
