ROTATION SPECTRUM AND STRUCTURE OF $CO_{2}-CO_{2}-H_{2}O$
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Date
1988
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Publisher
Ohio State University
Abstract
The microwave spectrum of the trimeric species $CO_{2}-CO_{2}-H_{2}O$ has been studied in the 718 GHz frequency range using a pulsed-molecular-beam Fabry-Perot Fourier transform microwave spectrometer. Only one set of b-type transitions are observed in contrast to the doubled set observed for $H_{2}O-H_{2}O-CO_{2}$. Using a centrifugal distortion Hamiltonian, these transitions can only be fit if the symmetric (ee-oo) and antisymmetric (eo-oe) set are analyzed separately. The rotational constants are: [FIGURE] The dipole moment for the complex is $\mu_{b}=1.989(2)D$. These observations imply that the complex has a two-fold axis of symmetry with the $H_{2}O$ subunit oriented such that its $C_{2v}$ axis is aligned with the b-axis of the complex. The magnitude of the rotational constants along with information obtained from $^{-13}C$ substitution suggest that the $CO_{2}$ subunits lie in a plane perpendicular to the b-axis separated by a distance similar to that observed in the $CO_{2}-CO_{2}$ dimer. It is expected that the oxygen of the $H_{2}O$ is oriented toward the plane of the two $CO_{2}$ subunits. The separation of the transitions into two sets suggests that each rotational level is shifted because of an internal motion. The most likely motion is interchange of the hydrogens in the $H_{2}O$ subunit. The levels are shifted rather than split because of the involvement of the $CO_{2}$ oxygens which have a spin quantum number of 0.
Description
Author Institution: Chemistry Department, Pastore Hall, University of Rhode Island; Molecular Spectroscopy Division, National Bureau of Standards