Study of the v1,v3 bands of 120SnH4: Part II--semiclassical qualitative analysis: critical phenomena and diabolic points

The qualitative modifications of the rovibrational energy-level structure under rotational excitation are studied for the (nu) 1 , (nu) 3 bands of 120 SnH 4 . Two types of qualitative changes are shown to exist: the critical phenomena corresponding to the modification of the cluster structure and the so-called diabolic points associated with the redistribution of energy levels between different branches as the rotational quantum number increases. A simple model interpretation of energy-level redistribution is given to show that such a phenomenon is typical for tetrahedral molecules.