Microwave Spectrum of Dimethylamine

Microwave spectra of 12 isotopic species of dimethylamine have been assigned for the ground vibrational state. Splittings arising from the inversion of the amino hydrogen have been observed and an inversion barrier of 4.4 kcal/mole has been estimated. From the rotational constants the structural parameters have been calculated and the conformation of the methyl groups has been determined. The structural parameters obtained are: $\mathrm{r(}\mathrm{CN}\text{)\hspace{0.17em}=\hspace{0.17em}1.466}\mathrm{\AA }\mathrm{,\; r(}\mathrm{NH}\text{)\hspace{0.17em}=\hspace{0.17em}1.022}\mathrm{\AA }\mathrm{,\; r(}\mathrm{CH}\mathrm{)\; (}\mathrm{average}\text{)\hspace{0.17em}=\hspace{0.17em}1.09}\mathrm{\AA }\mathrm{,\; \angle }\mathrm{CNC}\text{\hspace{0.17em}=\hspace{0.17em}112.2°, ∠}\mathrm{HCH\; (average)}\text{\hspace{0.17em}=\hspace{0.17em}108.6°, ∠}\mathrm{HNC}\text{\hspace{0.17em}=\hspace{0.17em}108.8°}$ . Evidence for an asymmetric methyl group is discussed. The ¹⁴N nuclear quadrupole coupling constants in the principal quadrupole axis system are ${\chi }_{\mathrm{xx}}\text{\hspace{0.17em}=\hspace{0.17em}3.04}\mathrm{MHz}{\mathrm{,\; \chi }}_{\mathrm{yy}}\text{\hspace{0.17em}=\hspace{0.17em}2.01}\mathrm{MHz}$ , and ${\chi }_{\mathrm{zz}}\text{\hspace{0.17em}=\hspace{0.17em}−5.05}\mathrm{MHz}$ , where the $x$ axis is normal to the symmetry plane. Analysis of the Stark effect gave a dipole moment of 1.01 D.