The rotational spectra of NH3–CO and NH3–N2

Abstract

The rotational spectra of NH3–CO, ND3–CO, ND2H–CO, NDH2–CO, NH3–13CO, and NH3–N2 have been measured by molecular beam electric resonance. The K=0 ground vibrational state transitions for these species were fit to a linear molecule Hamiltonian and the following constants were obtained for NH3–CO; (B+C)/2 (MHz)=3485.757(2), DJ (kHz)=110.2(2), eQqNaa (MHz)=−1.890(7), μa (D)=1.2477(8). These constants were also determined for ND3–CO [3078.440(7), 75.7(8), −2.028(15), 1.2845(9)], NHD2–CO [3202.303(4), 86.8(6), −1.972(11), 1.2686(8)], NH2D–CO [3338.235(4), 98.9(6), −1.916(12), 1.2546(8)], NH3–13CO [3451.684(5), 108.7(7), −1.870(15), 1.2452(8)]. For NH3–N2 (B+C)/2=3385.76(21), DJ =117.(10), and μa =1.069(14). For NH3–CO three ‖ΔJ‖=1, K=0 progressions were seen along with two ‖ΔJ‖=1, K=1 progressions, suggesting nonrigidity in the complex. The internal rotation of the NH3 subunit about its C3 axis is expected to be essentially free, but this motion, by itself, is not sufficient to explain the observed spectra, thus, large amplitude dynamics are occurring in at least two degrees of freedom. The quadrupole coupling constants, eQqNaa indicate that in each of the isotopes of NH3–CO the NH3 subunit has its C3 axis relatively rigidly oriented at an angle of approximately 36° with respect to the line connecting the centers of mass of the two subunits. The structure is not hydrogen bonded; the N atom is closest to the CO subunit. The orientation of the CO subunit is not established. The distance between the N atom and the center of mass of the CO unit (RN–CO) is 3.54(3) Å. The spectroscopic constants suggest that the weak bond stretching force constant is quite small (0.01 mdyn/Å) but compatible with the long bond length.