Diatomic molecule, orbitals electron configuration

A FIGURE 9.43 Molecular orbital electron configurations and some experimental data for period 2 diatomic molecules. 

Table 7.5 lists the states arising from a few electron configurations in diatomic molecules in which there are two electrons in the same degenerate orbital. 

Promotion of an electron in Hc2 from the (7 15 to a bonding orbital produces some bound states of the molecule of which several have been characterized in emission spectroscopy. For example, the configuration ((J l5 ) ((7 l5 ) ((7 25 ) gives rise to the 2i and bound states. Figure 7.24(a) shows the form of the potential curve for the state. The A-X transition is allowed and gives rise to an intense continuum in emission between 60 nm and 100 nm. This is used as a far-ultraviolet continuum source (see Section 3.4.5) as are the corresponding continua from other noble gas diatomic molecules. 

The ground-state electron configurations of diatomic molecules are deduced by forming molecular orbitals from all the valence-sbell atomic orbitals of the two atoms and adding the valence electrons to the molecular orbitals in order of increasing energy, in accord ivith the building-up principle. 

The molecular orbital energy-level diagrams of heteronuclear diatomic molecules are much harder to predict qualitatitvely and we have to calculate each one explicitly because the atomic orbitals contribute differently to each one. Figure 3.35 shows the calculated scheme typically found for CO and NO. We can use this diagram to state the electron configuration by using the same procedure as for homonuclear diatomic molecules. 

We can write configurations for diatomic molecules by naming the orbitals (cr, etc.), using superscripts to show how many electrons each orbital contains. Here is the configuration for the ground state of O2 ... 

In writing these configurations for diatomic molecules of second-row elements, we have omitted the electrons from the Is orbitals because they are not part of the valence shells of the atoms. When considering the oxygen molecule, for which the a orbital arising from the combinations of the 2pz orbitals lies lower in energy than the 7r orbitals, we find that the electron configuration is... 

If the electrons occupy orbitals different from the most stable (ground) electronic state, the bonding between the atoms also changes. Therefore, an entirely different potential energy surface is produced for each new electronic configuration. This is illustrated in Figure 6.6 for a diatomic molecule. 

The ground-state electron configurations of diatomic molecules are deduced by forming molecular orbitals from all the valence-shell... 

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