Flat Bottoms and Double Minimum Potentials

We assume at the bottom of a potential well a flattening of one degree of freedom, which simply becomes shallow, for example, for the bending of a triatomic molecule. The other two possible degrees of freedom still remain strong potential bowls, but the third degree acquires a nearly zero ascent. An example is the molecule LiNC (see literature in Ref.93), a long studied candidate for a polytopic molecule with 

If the path is not totally flat, as it may be the case looking at some microwave results, and LiNC in the isocyanide linear structure has a slight minimxim, then we arrive at a further example of a quantum cusp for the valley path of the large amplitude bending around the minimum (cf.Table 4 in Sect. 2.6.2). 

The most important member of a cuspoid, locally describing a onedimensional potential curve, is the cusp  

Gilmore et al. for a calculation of corresponding spectral bands. The tangent line in x =0 touches the curve in a higher order than 

The plane (c,a) is divided by the so called cusp-shaped curve, see Fig.13, which is a bifurcation set  

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