Critical phenomena and diabolic points in rovibrational energy spectra of spherical top molecules

Abstract

The qualitative modifications of the rovibrational energy-level structure under rotational excitation are studied for spherical top molecules. The ν2, ν4 bands of 12CD4 and 120SnH4 and the ν1, ν3 bands of 120SnH4 are treated as examples. 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. Manifestation of critical phenomena and diabolic point formation in high-resolution infrared spectra are discussed.