AN IAM FIT OF THE MICROWAVE SPECTRUM OF DIVINYL ETHER

$^{1}$ C. Hirose and R. F. Curi, Jr, J. of Mol. Spectrosc. 38, 358-366 (1971). $^{2}$ C. Hirose and S. Maeda, J. of Mol. Spectrosc. 72, 62-85 (1978). $^{3}$ J. T. Hougen, J. Mol Spectrosc. 114, 395-426 (1985). $^{4}$ W. Pyckhout, C. Van Alsenoy. H. J. Geise, B. Van Der Veken and G. Piaters. J. of Mol. Structure. 130, 335-353 (1985)Author Institution: Molecular Spectroscopy Division, National Bureau of StandardsDivinyl ether, $C_{2}H_{3}-O-C_{2}H_{3}$, occurs in two conformations, the trans-trans and the cistrans. The microwave spectrum of this latter conformer has been thoroughly measured by Hirose and $coworkers^{1-2}$, and reflects the effects of a 27 MHz tunneling splitting which appears especially for b and c type transitions. The tunneling motion responsible for the splitting correspond to an antigeared rotation of each vinyl unit about axes coinciding with the respective CO bonds. Because this problem is multidimensional, theory available at the time Hirose and $coworkers^{1-2}$ did their measurements was not adequate to obtain a satisfactory fit. Our goal is to improve this fit using new techniques. In this work we apply to the cis-trans conformer the IAM-like treatment $developed^{3}$ for multidimensional tunneling. The use of this method requires first the determination of the various paths connecting the two nonsuperimposable frameworks of the molecule. If this molecule goes through a planar configuration during the tunneling, we have one tunneling path. However, if the intermediate configuration is not planar, two equivalent tunneling paths will occur. The J and K dependence of the splittings in the case of a planar intermediate configuration is quite different from the dependence in the case of a nonplanar intermediate configuration. In our theory this dependence is characterized by three angles, $x_{p}, \theta_{p}$ and $\phi p$. Using this IAM formalism the microwave transitions were fit with an RMS deviation of 0.155 MHz and a determination of the value of the angles mentioned above was carried out. Even though one of them turned Out to be ill defined, the values obtained show that the cis-trans conformer of divinyl ether displays two tunneling paths. Starting from ab-initio data4 and guessing the equation of the tunneling path(s), a calculation of these angles was also undertaken theoretically