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Water in weak interactions: The structure of the water–nitrous oxide complex

1992; American Institute of Physics; Volume: 97; Issue: 5 Linguagem: Inglês

10.1063/1.463028

1520-9032

D. Zolandz, David Yaron, K. I. Peterson, William Klemperèr,

Spectroscopy and Laser Applications

The rotational spectra of H2O–N2O, D2O–N2O, and HDO–N2O have been observed using molecular beam electric resonance techniques at both zero and nonzero electric fields. H2O–N2O is nonrigid with respect to internal rotation of the water subunit. Rotational constants in MHz for the spatially antisymmetric tunneling state are A=12 605.001(77), B=4437.978(32), and C=3264.302(32). Rotational constants for the spatially symmetric tunneling state are A=12 622.595(203), B=4437.422(47), C=3264.962(47). These together with the rotational constants of the other isotopomers are consistent with a planar, T-shaped arrangement of the heavy atoms of the complex, with the distance between the centers of mass of the two subunits, Rc.m., equal to 2.91(2) Å or a distance of 2.97(2) Å from the H2O oxygen to the central nitrogen of N2O. The measured dipole moments of the two tunneling isomers are identical; μa = 1.480(2) and μb = 0.31(2) D. The values of these dipole moment components indicate an in-plane equilibrium tilt of about 20° between the C2v axis of water and the N–O weak bond. This tilt suggests a second interaction may exist between a hydrogen on water and the N2O subunit. The rotational constants suggest that the N2O unit is tilted by about 9° from perpendicular to the N–O weak bond. The barrier for the tunneling interchange of the water protons is estimated to be 235(10) cm−1. Quadrupole coupling constants eqQaa for the outer and inner nitrogen of N2O are 0.371(130) and 0.128(45) MHz, respectively. Electrostatic models applied to water–N2O and water–CO2 predict hydrogen bonded structures rather than the experimentally observed Lewis base structures.