MICROWAVE SPECTRUM AND STRUCTURE OF THE KETENE---ETHYLENE COMPLEX: AN EXAMPLE OF THE $2_{\pi} + 2_{\pi}$ CYCLOADDITION REACTION
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Date
1991
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Publisher
Ohio State University
Abstract
The microwave spectrum of the $CH_{2}CO---CH_{2}=CH_{2}$ complex was observed in a pulsed-beam Fourier transform microwave spectrometer. In addition to the normal isotopic species, which exhibits a b-type rotational spectrum and four states due to internal motions, complexes of ketene with trans-CHD$=$CDH and $CD_{2}=CH_{2}$ have been observed and these also exhibit four states, while the ketene---cis-CHD$=$CHD species exhibits two states. Spectral analysis yields the rotational constants for $CH_{2}CO---CH_{2}=CH_{2}:$ $A = 7494.141(2) MHz, B = 2276.441(6) MHz,$ and $C = 1966.992(6) MHz.$ The structural analysis, assuming fixed monomer geometries, show that the ketene unit lies in the a,b-plane of the complex and the symmetry axis of ethylene is parallel to the c-axis, i.e. the symmetry axis of the two units are crossed at $90^{0}$, with a center of mass separation, $R_{cm}$+ of 3.46 \.{A}. Stark effect measurements for the normal isotopic species provide the dipole moment components $ \mu a = 0$ D, $ \mu_{b} = 1.376(1)$ D and $ \mu_{c} = 0$ D which are consistent with the structural results. Further details concerning the tunneling motions and structure analysis will be given. Comparisons with related complexes, such as ketene--acetylene, and cycloaddition prototype species will be presented.
Description
Author Institution: Molecular Physics Division, National Institute of Standards and Technology; Department of Chemistry, Rensselaer Polytechnic Institute; Department of Chemistry, Siena College