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  • 1990-1994  (2)
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  • 1
    Electronic Resource
    Electronic Resource
    Structure, internal mobility, and spectrum of the ammonia dimer: Calculation of the vibration–rotation-tunneling states (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 8430-8442 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have obtained a potential for (NH3)2 by calculating the six-dimensional vibra- tion–rotation-tunneling (VRT) states from a model potential with some variable parameters, and adjusting some calculated transition frequencies to the observed far-infrared spectrum. The equilibrium geometry is strongly bent away from a linear hydrogen bonded structure. Equivalent minima with the proton donor and acceptor interchanged are separated by a barrier of only 7 cm−1. The barriers to rotation of the monomers about their C3 axes are much higher. The VRT levels from this potential agree to about 0.25 cm−1 with all far-infrared frequencies of (NH3)2 observed for K=0, ||K||=1, and ||K||=2 and for all the symmetry species: Ai=ortho–ortho, Ei=para–para, and G=ortho–para. Moreover, the dipole moments and the nuclear quadrupole splittings agree well with the values that are observed for the G states. The potential has been explicitly transformed to the center-of-mass coordinates of (ND3)2 and used to study the effects of the deuteration on the VRT states. The observed decrease of the dipole moment and the (small) changes in the nuclear quadrupole splittings are well reproduced. It follows from our calculations that the ammonia dimer is highly nonrigid and that vibrational averaging effects are essential. Seemingly contradictory effects of this averaging on its properties are the consequence of the different hindered rotor behavior of ortho and para monomers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468105
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    The nature of monomer inversion in the ammonia dimer (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 8443-8454 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A model is presented for calculating the splittings due to umbrella inversion of the monomers in (NH3)2. Input to the model are the six-dimensional dimer bound state wave functions for rigid monomers, calculated previously [E. H. T. Olthof, A. van der Avoird, and P. E. S. Wormer, J. Chem. Phys. 101, 8430 (1994)]. This model is based on first-order (quasi) degenerate perturbation theory and adaptation of the wave functions to the group chain G36⊆G72⊆G144. The umbrella inversion splittings depend sensitively on the intermolecular potential from which the bound state wave functions are obtained. A complete interpretation of the observed splitting pattern [J. G. Loeser, C. A. Schmuttenmaer, R. C. Cohen, M. J. Elrod, D. W. Steyert, R. J. Saykally, R. E. Bumgarner, and G. A. Blake, J. Chem. Phys. 97, 4727 (1992)] and quantitative agreement with the measured splittings, which range over three orders of magnitude, are obtained from the potential that reproduces the far-infrared spectrum of (NH3)2 and the dipole moment and nuclear quadrupole splittings of (NH3)2 and (ND3)2. The umbrella inversion splittings of (ND3)2 are predicted.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468106
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
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