On pseudorotation

Pseudorotation was introduced as a molecular motion related to degenerate ring deformation modes in ring systems. This motion is related to the motion of a particle on a ring and is, therefore, called a one-dimensional pseudorotation. This motion is related either to ring puckering or to the fluctuation of weak bonds. It is shown that there are systems where bond fluctuation occurs on the surface of polyhedra which are related to the motion of a particle on a sphere. We call these bond fluctuations two-dimensional pseudorotation and give the energy expressions for a free two-dimensional pseudorotation. One-dimensional pseudorotation is thoroughly discussed and shown how one can calculate the symmetry number of pseudorotation. We discuss systems where two-dimensional pseudorotation can be expected such as bullvalene or vacancies in solids with strong bond fluctuations.