APPLICATION OF CALCULATED DIPOLE MOMENT FUNCTIONS TO THE INTERPRETATION OF INFRARED INTENSITIES OF DIFLUOROETHYLENES.

This research was supported by National Science Foundation, Grant No. GP 8111. $^{1}$ J. A. Pople and G. A. Segal, J. Chem. Phys. 44, 3289 (1966). $^{2}$ G. A. Segal and M. L. Klein, J. Chem. Phys. 47, 4236 (1967). $^{3}$ G. A. Segal, R. Bruns and W. B. Person, J. Chem. Phys. 50, to be published (1969); R. Bruns and W. B. Person, unpublished results. $^{4}$ R. Kagel, Ph.D. Dissertation, University of Minnesota (1964). We are grateful to Professor J. Overend for the private communication of these experimental results.Author Institution: Department of Chemistry, University of FloridaWe have continued calculations of dipole moments of polyatomic molecules, as a function of their nuclear configuration, using the Pople and Segal CNDO approximate $method^{1}$ to obtain the molecular wave functions. Earlier $tests^{2, 3}$ have encouraged some confidence in the calculated results. Here we report calculated dipole moment derivatives for 1,1-difluoroethylene and cis 1,2-difluoroethylene and illustrate their application to the interpretation of the experimental infrared intensity data of Kagel and $Overend.^{4}$ These experimental results have been extremely difficult to interpret. For example, a typical symmetry class gives four to six possible sets of values for the dipole moment derivatives $(\partial\mu/\partial R_{j}$ where $R_{j}$ is a symmetry coordinate) which are consistent with all the experimental data, even from isotopically substituted molecules, depending upon the choice of relative signs for $\partial\mu/\partial Q_{i}$. Thus, interpretation of these data provides a real challenge for the theory. Use of these calculated dipole moment functions has been most encouraging and appears to be a major step forward in the interpretation of such experimental infrared intensity measurements