Internal Rotation in Completely Asymmetric Molecules. I. A General Theory and Analysis of the Microwave Rotational Spectrum of CH2DCOH, CD2HCOH, and CHOOCH2D

A theory for the internal rotation in molecules where the internal rotor is not a symmetric top has been formulated. The principal feature of the theory is the expansion of the rotational constants for the molecule in a converging series of sinnα and cosnα. This allows for the straightforward evaluation of certain integrals appearing in the development of the theory. In addition, the theory is applied specifically to CH2DCOH, CD2HCOH, and CHOOCH2D in the analysis of the microwave rotational spectra for these molecules. For CH2DCOH the height of the potential barrier hindering the internal motion is found to be V=410 cm—1, which is consistent with the barrier height for other species of acetaldehyde. To fit the spectra of CD2HCOH and CHOOCH2D a slight rotation of the effective principal axes must be made to obtain a consistent potential barrier. The results of the calculation indicate that (1) the theory is readily applicable in the determination of the barrier heights of the more general molecules, and (2) investigation of the deuterated-methyl internal rotors could provide information on the structure of the rotor.