Rotational constants ring-puckering effects

Fig. 4.5. Variation of the rotational constants (in MHz) with ring-puckering vibrational state for trimethylene oxide. The effect of the small barrier is quite dramatic when compared to the smooth variation in Fig. 2.5 for oxetanone-3.

If we restrict the Hamiltonian given by Eq. (3.10) to one vibrational coordinate, a ring-puckering coordinate with a constant effective mass, the following vibration-rotation Hamiltonian results... 

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