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Microwave and tunable far-infrared laser spectroscopy of the ammonia–water dimer

Stockman, Paul A. and Bumgarner, Roger E. and Suzuki, Sakae and Blake, Geoffrey A. (1992) Microwave and tunable far-infrared laser spectroscopy of the ammonia–water dimer. Journal of Chemical Physics, 96 (4). pp. 2496-2510. ISSN 0021-9606 http://resolver.caltech.edu/CaltechAUTHORS:STOjcp92

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Abstract

Microwave and far-infrared spectra of the H3N–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 V3=10.5±5.0 cm–1 for the barrier height to internal rotation for the NH3 monomer. A nonlinear equilibrium hydrogen bond is most consistent with the vibrationally averaged rotational constants; with the angle co^s–1[<lambdaz>] determined from <lambdaz>, 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^–1 is derived for the water tunneling motion about its c axis.


Item Type:Article
Additional Information:Copyright © 1992 American Institute of Physics (Received 14 August 1991; accepted 5 November 1991) This research was supported by grants from the Beckman Institute of Caltech, the NSF (CHEM-8957228), the Packard Foundation, and the Sloan Foundation. Acknowledgment is also made to the Donors of the Petroleum Research Fund, administered by the American Chemical Society, for partial support of this work. We thank P. G. Green for help in the data acquisition and for frequent discussions during the course of this work, T. R. Dyke and co-workers for sharing Ref. 34 prior to publication, F. Lovas for supplying us with his version of STRFTQ, and G. T. Fraser for helpful discussions. We also gratefully acknowledge the support and services rendered by the Caltech staff. Division of Geological and Planetary Sciences, California Institute of Technology, Contribution No. 5049.
Subject Keywords:AMMONIA; WATER; DIMERS; TUNING; FAR INFRARED RADIATION; LASER SPECTROSCOPY; MICROWAVE SPECTRA; SUPERSONIC FLOW; JETS; ROTATIONAL STATES; HYDROGEN BONDS; EQUILIBRIUM; LEAST SQUARE FIT; NONLINEAR PROBLEMS; MONOMERS; POTENTIAL ENERGY SURFACES; BARRIER HEIGHT; ION EXCHANGE; PROTONS; MOLECULAR CLUSTERS; INFRARED SPECTRA
Record Number:CaltechAUTHORS:STOjcp92
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:STOjcp92
Alternative URL:http://dx.doi.org/10.1063/1.462054
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:2246
Collection:CaltechAUTHORS
Deposited By: Archive Administrator
Deposited On:19 Mar 2006
Last Modified:26 Dec 2012 08:48

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