THE CORRELATION OF THE SYMMETRY CLASSIFICATIONS OF STATES OF NONRIGID MOLECULES

Abstract

The rovibronic and vibronic energy levels of some nonrigid molecules occur in nearly degenerate sets, whose splitting is due to tunneling between symmetrically equivalent regions of vibrational phase space. When the splitting is negligible, it is convenient to classify the different sets of energy levels according to a symmetry group that is determined by any one of the symmetrically equivalent regions, whereas when the splitting is appreciable, the individual split levels can be classified further according to a larger group that is determined in a similar way by a region containing all these equivalent regions. The former group is a subgroup of the latter.A simple correlation rule is proved, by means of which the symmetry species (in the larger group) of the individual split levels can be obtained from the symmetry species (in the smaller group) of the nearly degenerate set of levels. Some examples of the application of this rule to rovibronic and vibronic species are given.