Structure of the Methylamine Molecule. II. Theory of Internal Motions and Application to CD3ND2

A general theory is developed for the two low‐frequency internal motions which influence the microwave spectrum of methylamine. The interactions of the over‐all and internal rotations with the inversion motion are treated quantum‐mechanically for the case where the potential barriers to inversion and internal rotation are high. The theory justifies the method of analysis of the CD3ND2 spectrum which was given in paper I of this series. An expression is obtained for the empirical inversion parameters FKτ defined in I, and is shown to give an excellent fit of the experimental results for CD3ND2. The inversion splitting constant obtained from this calculation is 2246.0±5 Mc. The significance of this constant and of the other molecular parameters which enter the theory is discussed.