Molecular Structure of Methylamine

The matrix elements of the Hamiltonian of a semiasymmetric internal rotor which have been given by Hecht and Dennison are rederived in a different way and in a form which is also applicable to more general semiasymmetric internal rotors. This theory together with a semi-empirical formula for the inversion splitting is applied to the analysis of the microwave spectrum of methylamine. The barrier height of internal rotation is determined to be 691.1 cm -1 . The moments and product of inertia are obtained as A =37.085, B =38.662, C =8.136, C 1 =2.805, C 2 =5.331, D =-0.120 all times 10 -40 g cm 2 . The hypothetical inversion splitting in the absence of the coupling between inversion and internal rotation is determined to be 28604 Mc/sec for n =0 and 29358 Mc/sec for n =1. The molecular dimensions are obtained from the inertial constants as follows: d CH =1.093 A (assumed), d NH =1.014 A (assumed), d CN =1.474 A, \({=}109\)°30', \({=}105\)°50', \({=}112\)°10', and the methyl axis passes through the NH 2 triangle making an angle of 3°30' with the CN direction.