A new quantum number assignment is proposed for bendndash;stretch vibrational spectra with 2:1 Fermi resonance. Using a classification based on the catastrophe map and polyad phase spheres of the Fermi resonance fitting Hamiltonian, quantum numbers are assigned corresponding to the semiclassical dynamics of each energy level. The method is applied to assign experimental spectra of CH(CF3)3. The separability of the wave functions is discussed in terms of lsquo;lsquo;nodal coordinatesrsquo;rsquo; for which the new quantum numbers are constants of the motion.
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