The rotational spectrum, barrier to internal rotation, and structure of NH₃-N₂O

The rotational spectrum of NH₃-N₂O has been observed by the molecular beam electric resonance method. The spectrum is characteristic of a T-shaped complex in which the nitrogen of the NH₃ subunit is directed toward the N₂O subunit. The NH₃ unit exhibits nearly free internal rotation about its C₃ axis. The A internal rotor state transitions were fit to Watson's asymmetrical top Hamiltonian and the following spectroscopic constants were determined: A(MHz) = 12 722.5(5), δ_K(MHz) = 0.22(2), B(MHz) = 4 083.5(2), δ _J(MHz) = 0.007(1), C(MHz) = 3 070.8(2), Δ_K(MHz) = -0.3(2), Δ_J(MHz) = 0.016(9), Δ_JK(MHz) = 0.32(3), μ_a(D) = 1.514(9), μ_b(D) = 0.09(9). The E internal rotor state transitions were fit to the Hamiltonian of Kilb, Lin, and Wilson. For the E internal rotor state the rotational constants A [12 743(64) MHz], B [4077.1(12) MHz], and C [3069.9(9) MHz] were determined, as well as the height of the barrier to internal rotation, V₃ [12.5(25) cm ^-1]. The distance between the nitrogen of the NH₃ to the center of mass of N₂O is 3.088 Å. The angle between the C ₃ axis of NH₃ and the line joining the centers of mass of the NH₃ and N₂O subunits is 13̊. The C₃ axis of NH₃ is pointed towards the nitrogen end of the N₂O subunit.