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

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.