THE MICROWAVE SPECTRUM OF VINYL $IODIDE^{*}$
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Date
1954
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Ohio State University
Abstract
Of 69 transitions which have been observed in the 24,000-to-25,800-Mc region of the microwave spectrum of vinyl iodide, 28 have been assigned as the $J= 3 \rightarrow 4$ transitions $3_{03}\rightarrow 4_{04}$, $3_{13}\rightarrow 4_{14}$, and $3_{12}\rightarrow 4_{13}$. Confirmation of this assignment was obtained from the quadrupolar hfs, Stark effect, temperature coefficient of intensity, and relative intensities of the various lines. Although first-order perturbation theory was adequate to predict the general form of the quadrupolar hfs pattern, it was necessary to take into account second-order effects to obtain a precise agreement between observed and calculated frequencies. The quadrupolar constants for the two transitions with $K_{-1}=1$ agree reasonably well, so that on this basis the average value of these constants could be taken as $\chi_{{aa}}=-1645\pm 5$ Mc and $\chi_{bb}=+764\pm 9$ Mc. The apparent disagreement of the $\chi_{aa}, \chi_{bb}$ values for the $3_{03}\rightarrow 4_{04}$ transition with those for the two $K_{-1}=1$ transitions is not surprising when one observes that the first-order quadrupolar energy terms are quite insensitive to $\chi_{bb}$ for this transition. Of the magnetic constants, only ${b}$ is well determined; ${a}$ is rather uncertain. From the observed quadrupole coupling constants, the components of $eQV^{2} V$ along the C-I bond are computed as $\chi_{zz}=-1869$ Mc, $\chi_{yy}=+988$ Mc, and $\chi_{xx}=+882$ Mc, where ${y}$ and ${z}$ are in the molecular plane. In terms of these components, the C-I bond asymmetry is $\eta=0.057$ which is of the same order of magnitude as is found for vinyl chloride and vinyl bromide.
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$^{*}$This work was supported in part by ONR Contract N8-onr-79400. $^{**}$Present address: Chemistry Department, University of Wisconsin, Madison, Wisconsin. $^{\dagger}$DuPont Predoctoral Fellow. Present address: Department of Physics, Ohio State University, Columbus, Ohio.
Author Institution: Department of Chemistry, The State University of Iowa
Author Institution: Department of Chemistry, The State University of Iowa