1B 1 u 5
4A 1 u 1 þ u 2 þ u 7 À u 4
2B 2 u 1 À u 2 þ u 6
The numbers before the symmetry indicate the progression of orbitals of a given
symmetry. The grey color indicates the negative sign of the function.
In the case we tentatively adopt a linear D ∞h symmetry (Scheme 2.4), the
irreducible representation will be 2r g , 1r u , p u , 3r g , 2r u , a lower number than for
the C 2v , due to degeneracy of p u . The lack of p u induces stabilization of 3a 1 .
The HOH angle of 105.5° amplitude is the best convenient to minimize the
energy of the water molecule. Scheme 2.5 reported the energy trend (A) and the H–
O binding energy (B) against HOH angle.
The photoelectron spectrum of the water molecule (Fig. 2.1) confirms the
symmetry energy trend, excluding the presence of degenerate p u states.
bent
2b 2
2a 1
4a 1
3a 1
1b 1
1b 2
2p
E
2H
2σ υ
1s
2s
3σ g
linear
1л υ
1σ υ
O
2σ g
Scheme 2.4 H 2 O linear
symmetry versus the bent one
(the real one)
2.2 Water Molecule, as Example of Triatomic Molecule
31
4A 1 u 1 þ u 2 þ u 7 À u 4
2B 2 u 1 À u 2 þ u 6
The numbers before the symmetry indicate the progression of orbitals of a given
symmetry. The grey color indicates the negative sign of the function.
In the case we tentatively adopt a linear D ∞h symmetry (Scheme 2.4), the
irreducible representation will be 2r g , 1r u , p u , 3r g , 2r u , a lower number than for
the C 2v , due to degeneracy of p u . The lack of p u induces stabilization of 3a 1 .
The HOH angle of 105.5° amplitude is the best convenient to minimize the
energy of the water molecule. Scheme 2.5 reported the energy trend (A) and the H–
O binding energy (B) against HOH angle.
The photoelectron spectrum of the water molecule (Fig. 2.1) confirms the
symmetry energy trend, excluding the presence of degenerate p u states.
bent
2b 2
2a 1
4a 1
3a 1
1b 1
1b 2
2p
E
2H
2σ υ
1s
2s
3σ g
linear
1л υ
1σ υ
O
2σ g
Scheme 2.4 H 2 O linear
symmetry versus the bent one
(the real one)
2.2 Water Molecule, as Example of Triatomic Molecule
31