THE 3700 {\AA} $n-\pi^{*}$ TRANSITION OF PYRIDAZINE
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Date
1977
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Ohio State University
Abstract
Among the better-resolved rotational band contours of electronic spectra of aromatic molecules are those of type C bands near the origin of the $1_{B_{1}}-1_{A_{1}}$ transition of 1,2-diazine. Because microwave studies have provided inertial constants for the $1_{A_{1}} (v - 0)$ level, these bands offer interesting tests of maximum reliability for computer simulations of band contours of near-oblate asymmetric rotors. The most definitive result of such tests is found by comparing contour analyses of the $0-0$ and ${6a}^{0}_{1}$ bands; it is shown that the effect of excitation of one quantum of $\nu^{\prime\prime}_{6a}$ is to approximately equalize the two in-plane moments of inertia, by Increasing the moment about the symmetry axis and decreasing the other moment, each by about 2.3%. On the other hand, two solutions are found for the effect of electronic excitation. In both, the directions of changes of moments are the same as for excitation of $\nu_{6a}$. One solution is for an increase of the moment about the symmetry axis by 2% and a decrease of the other moment by 1.5%. The second solution uses the same upper-state moments but switches the one associated with the symmetry axis so that the changes are by +3.3% and $-$2.9%, respectively. Even these larger changes are appreciably smaller than those found recently for the analogous electronic change of the s-tetrazine $molecule.^{1}$ Implications of these and other observations will be discussed.
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$^{1}$R. E. Smalley, L. Wharton, D. H. Levy, and D. W. Chandler, J. Mol. Spectrosc, (in press). This work was supported by the National Science Foundation.
Author Institution: Department of Chemistry, State University of New York
Author Institution: Department of Chemistry, State University of New York