Rotational spectroscopic studies of weakly bound complexes of NH3

Radiofrequency and microwave spectra of NH3-CO and NH3-2O have been measured using the molecular beam electric resonance technique. For NH3-N2O an asymmetrical top spectrum is observed and is complicated by internal rotation of the NH3 subunit. The rotational constants for the ground internal rotor state are: A = 12722.6(8) MHz, B = 4083.4(3) MHz, and C = 3070.8(3) MHz. NH3-N2O is a T-shaped complex with a N-N weak bond length of 3.2 A. The electric dipole moment component along the a-inertial axis is 1.514(9) D. Attempts are presently underway to determine the height of the threefold barrier to internal rotation. It should be noted that the structurally similar complex, NH3-CO2, has no threefold barrier. The K = O J = 0.1, 1-2 transitions have been observed for NH3-CO, NH2D-CO, NHD2CO, ND3-CO, NH3-13CO. The observed isotopic dependence of the rotational constants is consistent with a structure which has the nitrogen directed toward the carbon. The spectrum is complicated by non-rigidity and is not completely understood. The structure determined from the K = O transitions is consistent with the orientation of amine-carbonyl groups observed in organic crystals