Microwave spectrum, tunneling motions, and quadrupole coupling hyperfine structure of ethylene diamine

New transitions are measured in the microwave spectrum of two conformers of the non-rigid ethylene diamine (CH2NH2-CH2NH2) molecule using both molecular beam Fourier transform and stark modulation spectroscopy. Ab initio calculations are carried out to obtain geometries and energies for several stationary points of the potential energy surface and to gain quantitative information on the tunneling paths along which the molecule tunnels. The microwave data are reproduced using an IAM-like approach which accounts for the rotational dependence of the tunneling splitting corresponding to the interconversion large amplitude motion. For one of the conformers, the results of this analysis are consistent with the ones obtained through ab initio calculations. Hyperfine patterns are analyzed with the help of a theoretical approach accounting for the large amplitude motion effects and for hyperfine matrix elements within and between tunneling sublevels.