Barrier height inversion splitting

Inversion splittings can be observed for the formaldehyde molecule in its electronically excited A A2 and a3A2 states because the molecule adopts a nonplanar equilibrium structure. In the former, the angle between the C-O bond and CH2 plane is 34°, and the barrier height for inversion is 350 cm 1 (1.00 kcal/mol), while in the latter this angle increases to as much as 41° and the barrier height, correspondingly, increases to 775 cm-1. The potentials obtained by Jensen and Bunker... 

We have already seen in Section 2 how barriers to inversion are obtained from the energy level splittings due to quantum mechanical tunneling. In this case the shape and the height of the potential curve are obtained by fitting the calculated splittings to the observed ones using Eq. (5) and (6). 

We shall divide these molecules into two categories (i) molecules with one large amplitude motion (inversion) which will be dealt with in Section 6.1 (ii) molecules with inversion and internal rotation (Section 6.2). Only such molecules will be considered, where the inversion barrier is low enough that inversion splittings can be resolved by microwave or infrared spectroscopy. As for the pyramidal inversion with higher barriers, description of the methods for determination of the barrier heights and the chemical consequences of the existence of the so-called invertomers, the reader is referred to review papers ... 

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