Chemistry Reference
In-Depth Information
D
E bond energies (10
3
E
h
) for the ground state of simple homonuclear
Table 9.1
diatomics
2
g
1
g
2
u
H
2
He
2
R
/
a
0
ð
Þ
H
2
ð
Þ
ð
Þ
S
S
S
1
59.001 6
88.585 2
570.468 1
15.921 6
128.956 1
1.2
223.806 2
55.339 8
139.049 5
1.4
46.991 8
75.319 2
134.372 6
39.864 2
1.6
1.8
84.176 4
122.673 4
78.053 4
2
86.506 0
108.010 1
89.992 0
3
64.448 2
41.699 3
46.940 5
4
37.334 5
11.358 2
13.819 3
5
19.205 4
2.534 91
3.421 80
6
9.080 4
0.509 89
0.783 36
To investigate the origin of the chemical bond, optimized VB calcula-
tions were done (Magnasco, 2008) for the ground states of H
2
2
g
ð
S
Þ
,
u
Þ
, a series of simple molecules that are the
prototypes of one-, two- and three-electron
1
g
and He
2
2
H
2
ð
S
Þ
ð
S
chemical bonds, and of
the Pauli repulsion for theHe(1s)-He(1s) interaction. The bond energy
s
D
E
D
E
cb
and exchange-overlap
D
E
exch-ov
components, the Coulombic component being best obtained
by direct analytical calculation avoiding the round-off errors that would
arise at the larger distances.
A summary of the results
5
is presented in Tables 9.1-9.4. For all systems
studied, including the molecule-ions H
2
and He
2
, the Coulombic
component (Table 9.2) has a charge-overlap nature rapidly decreasing
is analysed into its polarized Coulombic
D
E
cb
Coulombic component (10
3
E
h
) of the bond energies for the ground
state of simple homonuclear diatomics
Table 9.2
H
2
He
2
R/a
0
H
2
1
117.092 9
15.846 9
41.179 9
1.2
68.997 0
9.928 7
5.603 9
1.4
42.746 1
19.423 1
14.892 8
1.6
27.486 5
21.831 1
13.535 4
1.8
18.173 0
21.076 3
9.975 0
2
12.260 2
18.993 9
6.709 6
3
2.005 7
7.016 22
0.522 67
4
0.341 95
1.677 58
0.026 28
5
0.053 3
0.329 08
0.001 10
0.060 06
0.000 04
6
0.007 5
5
The optimized values of the orbital exponent c
0
at the various R are given inMagnasco (2008).
