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.