Triatomic molecules notations

In this section, we briefly discuss spectroscopic consequences of the R-T coupling in triatomic molecules. We shall restrict ourselves to an analysis of the vibronic and spin-orbit structure, determined by the bending vibrational quantum number o (in the usual spectroscopic notation id) and the vibronic... 

An important problem of molecular spectroscopy is the assignment of quantum numbers. Quantum numbers are related to conserved quantities, and a full set of such numbers is possible only in the case of dynamical symmetries. For the problem at hand this means that three vibrational quantum numbers can be strictly assigned only for local molecules (f = 0) and normal molecules ( , = 1). Most molecules have locality parameters that are in between. Near the two limits the use of local and normal quantum numbers is still meaningful. The most difficult molecules to describe are those in the intermediate regime. For these molecules the only conserved vibrational quantum number is the multiplet number n of Eq. (4.71). A possible notation is thus that in which the quantum number n and the order of the level within each multiplet are given. Thus levels of a linear triatomic molecules can be characterized by... 

Figure 13. Spectrum of a planar triatomic molecule in the local limit. N = 100, A = -3 cm , and A = 3 cm . (t)j, v, v,) is the degeneracy local mode notation (see the text). The degeneracy associated with the true local mode basis appears in brackets, p is the total number of stretching vibrational quanta in a given polyad.

---