Correlation diagrams for rigid and nonrigid four-body systems

Abstract

Correlation diagrams are constructed to connect the rotation–vibration energy levels of idealized limiting models for the tetratomic molecule. One limit is the completely nonrigid homonuclear four‐atom cluster. Several choices are taken for the other limit: the nearly rigid regular tetrahedron and square, the dimer of two identical homonuclear diatomics, and the ammonialike inverter. A dimensionless parameter, the ratio of two energies, is proposed to characterize the degree of nonrigidity for molecules of arbitrary size or complexity. The parameter is evaluated for several examples.