Knowledge Bank

The fundamental transition of the torsional motion around the central C-C bond in pyruvic acid $(CH3COCOOH)$ occurs at nearly the same frequency as that of the methyl torsion. The rotational spectrum of the first excited state of the skeletal mode showed effects of a strong coupling with the methyl torsion. For rotational transitions the sign and magnitude of the A-E splittings due to the methyl torsion is different in this state from those of the ground and higher excited states. This observation is in good agreement with model results obtained by a new technique for intramolecular motion with two degrees of $freedom.1$ The A-E splittings in ground and several excited states could be predicted from appropriate differences of calculated eigenvalues.