Spin-orbit interaction orthogonality properties

Relativistic corrections make significant impact on the electronic properties of heavy atoms and molecules containing heavy atoms. The inner s orbitals are the closest to the nucleus and thus experience the high nuclear charge of the heavy atoms. Thus, the inner s orbitals shrink as a result of mass-velocity correction. This, in turn, shrinks the outer s orbitals as a result of orthogonality. Consequently, the ionization potential is also raised. The p orbitals are iilso shrunk by mass-velocity correction but to a lesser extent since the angular momentum keeps the electrons away from the nucleus. However, the spin-orbit interaction splits the p shells into pi/2 and pj/2 subshells and expands the P3/2 subshells. The net result is that the mass-velocity and spin-orbit interactions tend to cancel for the P3/2 shell but reinforce for the Pi/2. 

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