Knowledge Bank

Methyl amine, methyl amine-$d2$, methy-$d3$ amine and methyl-$d3$ amine-$d2$ of high chemical and isotopic purity have been synthesized and their infrared spectra studied at both prism and grating resolution. The vibration-rotation band centers of methyl amine have been measured with improved accuracy over previous investigations and with the aid of the spectra of the deuterium analogs a vibrational assignment differing in some important respects from those hitherto suggested has been made. The grating spectra in some cases show irregularities in the rotational fine structure but none which can be associated with effects due to hindered internal rotation. Recent studies in the microwave region have shown that these effects should not be observed within the resolution limits of the grating spectrometers used in this work. However the first overtone of the torsional frequency in methyl amine, methyl amine-$d2$ and methyl-$d3$ amine has been observed in a position consistent with calculations based on a barrier height of $690cm-1$. The rotational structure of a number of unperturbed vibrational bands has been analyzed in terms of equations applicable to an approximate symmetric top and rotational constants have been obtained in good agreement with values calculated from parameters obtained from microwave investigations.