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

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: χ_aa=0.67±0.02, χ_bb=2.24±0.02, χ_cc=−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.