Microwave Spectra of Nitrogen-Containing Molecules. III. Structure, Dipole Moment, Quadrupole Coupling Constants, and Barrier to Internal Rotation of trans-Propyleneimine

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Abstract
The microwave spectrum of trans‐propyleneimine has been studied in the ground state and the first excited state of the methyl torsion. Ground‐state rotational constants for the normal isotopic species and for the C3H6N—D species are as follows: A = 16 892.59, B = 6533.63, C = 5761.37 and A = 16 082.31, B = 6338.70, C = 5537.81 MHz, respectively. The height of the barrier to internal rotation has been found to be 2608±26 cal/mole by analysis of splittings of ground‐state and first excited‐state lines. Measurements of the Stark effect have led to a total dipole moment of 1.57 D, and analysis of hyperfine structure has given the quadrupole coupling constants of the 14N nucleus: χaa=0.67±0.02, χbb=2.24±0.02, χcc=−2.91±0.01 MHz. An estimate has been given of the quadrupole coupling constants in the principal axis system of the electric‐field‐gradient tensor, and the molecular structure has been discussed.