Infra-Red Bands of Methylamine and the Phenomenon of Free Rotation

Two bands in the absorption spectrum of methylamine have been measured in the photographic infra-red. One of the bands shows rotational structure. The bands have been interpreted as involving excitation of the frequencies 3νCH+νCN). The rotational structure of the latter band suggests that it is a perpendicular-type band, and the precise spacing of the Q branches suggests that the molecule behaves approximately like a rigid symmetric top. The inference of hindered internal rotation is in agreement with other independent data.