Knowledge Bank

“A number of molecules of the type ($CH3)3AB$ have been investigated in the microwave region. In those cases where the internal rotation of the $CH3$ groups is strongly hindered, the spectra are found to follow symmetric-rotor patterns. These patterns have been analyzed in detail for ($CH3)3N,(CH3)3P,(CH3)3CH$, and $(CH3)3CF$. Rotational transitions in a number of exeited vibrational states, including those associated with the $CH3$ torsional modes, have been identified, and the vibrational frequencies have been determined from relative intensity measurements. The torsional frequencies have been used to derive information on the potential function for internal rotation. In these four molecules the potential terms which involve coupling among the three $CH3$ groups are found to be relatively small. The effects of I-type doubling in degenerate vibrational states of these molecules have also been analyzed. Molecular structures have been determined with the aid of $C14$ isotopie species, and electric dipole moments have been measured from the Stark effects. The trends in these molecular parameters will be discussed.”