Microwave and far-infrared spectra of the H, N-HOH dimer have been recorded from 36 to 86 GHz and 520 to 800 GHz with a planar supersonic jet/tunable laser sideband spectrometer. The a-type pure rotational microwave data extend the previous m = 0, K = 0 A symmetry manifold measurements of Herbine and Dyke [J. Chem. Phys. 83, 3768 ( 1980) ] to higher frequency and also provide an additional set of microwave transitions in the mK = + 1 E symmetry manifold. Two sets of five b-type rotation-tunneling bands, one set shifted from the other by an approximately constant 113 MHz, have been observed in the far infrared. The splitting into two sets arises from water tunneling, while the overall band structure is due to internal rotation of the ammonia top. Nonlinear least-squares fits to an internal rotor Hamiltonian provided rotational constants, and an estimation of V, = 10.5 f 5.0 cm-' for the barrier height to internal rotation for the NH, monomer. A nonlinear equilibrium hydrogen bond is most consistent with the vibrationally averaged rotational constants; with the angle cos-'[(A,)] d e t ermined from (A,), the projection of the ammonia's angular momentum onto the framework; and with the nitrogen quadrupole coupling constants of Herbine and Dyke. The water tunneling splitting and observed selection rules place constraints on the barrier height for proton exchange of the water as well as the most feasible water tunneling path along the intermolecular potential energy surface. An estimated barrier of -700 cm -' is derived for the water tunneling motion about its c axis.

O between 7 and 24 GHz using a Fourier-transform microwave spectrometer. Because CH 3 OH and H 2 O are capable of both accepting and donating hydrogen bonds, there exists some question as to which donor-acceptor pairing of the molecules is the lowest energy form. This question is further emphasized by the ambiguity and variety present in previous experimental and computational results. Transitions arising from the methyl torsional A state were assigned in each of the studied isotopomers, and for the A and E states in , where the errors correspond to 1 uncertainties-are consistent with either conformation, the fit of the structure to the rotational constants demonstrates unambiguously that the lower-energy conformation formed in supersonically cooled molecular beams corresponds to a water-donor, methanol-acceptor complex. The results and implications for future work are also discussed in terms of the permutation-inversion theory presented by Hougen and Ohashi ͓J. Mol. Spectros. 159, 363 ͑1993͔͒.

No abstract

Several far-infrared vibration-rotation-tunneling transitions have been measured in deuterated isotopomers of Ar–H2O for the first time. These experimental results will enable the generation of improved intermolecular potential energy surfaces for the Ar–H2O system when combined with existing microwave, far-infrared, and infrared data.

No abstract