Blake, Geoffrey A. and Busarow, Kerry L. and Cohen, R. C. and Laughlin, K. B. and Lee, Y. T. and Saykally, R. J. (1988) Tunable far-infrared laser spectroscopy of hydrogen bonds: The K_a = O(u)→1(g) rotation-tunneling spectrum of the HCI dimer. Journal of Chemical Physics, 89 (11). pp. 6577-6587. ISSN 0021-9606 http://resolver.caltech.edu/CaltechAUTHORS:20120601-080012884
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The ground state K_a =0(u)→1(g) b‐type subband of the rotation–tunneling spectrum of the symmetric ^(35)Cl–^(35)Cl,^(37)Cl–^(37)Cl, and the mixed ^(35)Cl–^(37)Cl hydrogen chloride dimers have been recorded near 26.3 cm^(−1) with sub‐Doppler resolution in a continuous two‐dimensional supersonic jet with a tunable far‐infrared laser spectrometer. Quadrupole hyperfine structure from the chlorine nuclei has been resolved. From the fitted rotational constants a (H^(35)Cl)_2 center‐of‐mass separation of 3.81 Å is derived for the K_a =1(g) levels, while the nuclear quadrupole coupling constants yield a vibrationally averaged angular structure for both tunneling states of approximately 20–25 deg for the hydrogen bonded proton and at least 70–75 deg for the external proton. This nearly orthogonal structure agrees well with that predicted by ab initio theoretical calculations, but the observed splittings and intensity alterations of the lines indicate that the chlorine nuclei are made equivalent by a large amplitude tunneling motion of the HCl monomers. A similar geared internal rotation tunneling motion has been found for the HF dimer, but here the effect is much greater. The ground state tunneling splittings are estimated to lie between 15–18 cm^(−1), and the selection rules observed indicate that the trans tunneling path dominates the large amplitude motion, as expected, provided the dimer remains planar. From the observed hyperfine constants, we judge the dimer and its associated tunneling motion to be planar to within 10°.
|Additional Information:||© 1988 American Institute of Physics. Received 10 June 1988; accepted 16 August 1988. This work was supported by the Director, Office of Energy Research, Office of Basic Energy Sciences, Chemical Sciences Division of the U. S. Department of Energy under Contract No. DE-AC03-76SF00098. The FIR laser system was funded by the National Science Foundation (Grant CHE-8612296) and by the Army Research Office-University Research Instrumentation Program (Grant DAAL03-86-G-0184). The authors thank H. M. Pickett for useful discussions and for providing the multispin Hamiltonian program. G. A. B. gratefully acknowledges financial support from the Berkeley Miller Basic Research Institute.|
|Subject Keywords:||MOLECULAR CLUSTERS, HYDROGEN BONDS, HYDROCHLORIC ACID, DIMERS, INFRARED SPECTRA, LASER SPECTROSCOPY, HYPERFINE STRUCTURE, CHLORINE 35, COUPLING CONSTANTS, CHLORINE 37, CHEMICAL BONDS, ADDUCTS, CHLORINE|
|Classification Code:||PACS: 33.20.Ea, 36.40.-c, 33.15.Mt, 33.15.Pw|
|Official Citation:||Tunable far‐infrared laser spectroscopy of hydrogen bonds: The Ka =0(u)→1(g) rotation–tunneling spectrum of the HCl dimer Geoffrey A. Blake, Kerry L. Busarow, R. C. Cohen, K. B. Laughlin, Y. T. Lee, and R. J. Saykally J. Chem. Phys. 89, 6577 (1988); http://dx.doi.org/10.1063/1.455380|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||01 Jun 2012 15:24|
|Last Modified:||26 Dec 2012 15:17|
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