146CHAPTER 5 Symmetry and Molecular OrbitalsBdenotes a nondegenerate orbital or state that is antisymmetric around that axis. Eand Tdenote doubly and triply degenerate states, respectively. Subscripts 1 and 2 indicate symmetry or antisymmetry, respectively, with respect to a rotation axis other than the principal axis of symmetry. In Chapter 3, the molecular orbital approach was used to describe the bonding in diatomic molecules. When considering more complicated molecules, the molecular orbital approach is more complicated, but the use of symmetry greatly simplifies the process of constructing the energy level diagrams. One important aspect of the use of symmetry is that the symmetry character of the orbitals used in bonding by the central atom must match the symmetry of the orbitals on the peripheral atoms. For example, the combination of two hydrogen atom 1 swave functions, φ1s(1) φ1s(2), transforms as A1(or a1if molec-ular orbitals are described), but the combination φ1s(1) φ1s
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