Bonding in Homonuclear Diatomic Molecules

The simple molecular orbital theory of bonding in homonuclear diatomic molecules can be used to estimate the electron affinities of clusters. In these cases, there can be different geometries. The Cn clusters have been studied most extensively. In the case of the triatomic molecules, there are now two distances and one angle that... 

For a molecule to absorb infrared radiation, the bond rmdergoing vibration must be polar, and its vibration must cause a periodic change in the bond dipole the greater the polarity of the bond, the more intense is the absorption. Any vibration that meets this criterion is said to be infrared active. Covalent bonds in homonuclear diatomic molecules, such as Hg and Br2, and some carbon-carbon double bonds in symmetrical alkenes and alkynes do not absorb infrared radiation because they are not polar bonds. The multiple bonds in the following two molecules, for example, do not have a dipole moment and, therefore, are not infrared active ... 

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