Hybridization and Bonding in Polyatomic Molecules

In organic chemistry, s-p hybridization is an important qualitative concept in the description of chemical bonds. Optimum orbitals for bonding in linear, planar trigonal, and tetrahedral configurations are formed by sp, sp, and sp hybrids. We have previously discussed how hybridization may be influenced by spin-free relativistic effects. With the involvement of p spinors that may be highly spin-orbit split, hybridization will also be influenced by the spin-orbit coupling. 

For linear molecules, we can form sp hybrids from the spinors  

For molecules such as these, the spin-orbit effect is essentially quenched in the molecule, because to exist it must form a strong bond, and the spin-orbit splitting is not so large that the quenching cannot be achieved. This is obvious for light atoms such as C and Si, but even Pb(C2H5)4 has four equivalent sp hybridized bonds. We can 

The superheavy elements are beyond the quenching regime, however, and the spin-orbit effect is so large that it is not quenched. In HUus, for example, the lp /2 shell contracts significantly and forms an inert pair, leaving an unpaired 7p3/2 electron to form an s-p j bond, which is weaker than a regular a bond and contains a significant lone-pair component (Saue et al. 1996). 

The capability for relativistic hybridization is present for molecules of other than linear symmetry. The symmetry spinors for groups lower than cubic can be classified in terms of the m.j quantum numbers for spinors at the high symmetry point (or axis). Since the j quantum number is not part of the classification, relativistic hybridization can always take place. For example, in Dih the fermion irreps are e /2, e ji, and es/2, for which the Kramers partners have Tw modb = 1/2, 3/2, 5/2, respectively. The i and j = l + j spinors for a given rtij both belong to the same irrep. In 

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