Microwave Spectra of Molecules Exhibiting Internal Rotation. III. Trimethylamine

The first two rotational transitions of trimethylamine have been studied. The spectrum of the ground vibrational state follows a symmetric‐rotor pattern with the following constants: $$B_0\text{=8720.86\hspace{0.17em}}\mathrm{Mc}{\mathrm{,\hspace{0.17em}\hspace{0.17em}D}}_J\text{=5\hspace{0.17em}}\mathrm{kc}\mathrm{,\hspace{0.17em}\hspace{0.17em}eqQ(}{\mathrm{N}}^{14}\text{)=−5.47\hspace{0.17em}}\mathrm{Mc}\text{,\hspace{0.17em}\hspace{0.17em}μ=0.612\hspace{0.17em}}\mathrm{D}.$$ If a reasonable structure is assumed for the CH₃ groups, the framework structure is found to be: r_CN=1.472 A, ≤CNC=108.7°. The satellite lines which surround each ground‐state transition have been assigned to excited vibrational states. Relative intensity measurements on these satellites lead to frequencies of 263 cm^—1 and 290 cm^—1 for the torsional modes of species A₂ and E, respectively. These frequencies are interpreted in terms of a simplified model for the torsional motions of the methyl groups. The implications of the results are discussed.