THE VAN DER WAALS TRIMER, $AR_{2}$KETENE
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Date
1998
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Ohio State University
Abstract
The rotational spectrum of the oblate asymmetric top van der Waals trimer, $Ar_{2}$-ketene, was obtained with a pulsed-beam Fourier-transform microwave spectrometer. Two tunnelling states arising from internal rotation of ketene were assigned for $Ar_{2}CH_{2}CO$ and $Ar_{2}CD_{2}CO$. The least squares fit of the observed $\mu_{b}$ and $\mu_{c}$-type transitions of the ground state normal isotopomer to a semirigid Watson Hamiltonian gave rotational constants of $A = 1652.28376(17)MHz. B = 1484.42510(16)MHz$ and $C = 914.02182(37)MHz$. Electric dipole moment components of $\mu_{b} = 0.175(18)D$ and $\mu_{c} = 1.343(3)D$ were calculated from Stark shift measurements of the ground state normal isotopomer. The spectral data are consistent with a trimer structure in which the CCO axis of ketene is perpendicular to the Ar-Ar axis. Least squares fits of the moments of inertia of the two isotopomers gave an Ar-Ar separation of 1.916(2){AA}, a ketene center of mass to the Ar-Ar bisector of 3.039(5){\AA} and an angle of $99.5(1.5)^{\circ}$ between the methylene carbon, center of mass of ketene and the point at the bisector of the Ar-Ar separation.
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Author Institution: Department of Chemistry, Rensselaer Polytechnic Institute; Department of Chemistry, Siena College