1. ANALYSIS OF THE ROTATIONAL STRUCTURE IN THE HIGH-RESOLUTION INFRARED SPECTRA OF cis,cis- AND trans,trans-1,4- DIFLUOROBUTADIENE-1-d 1 AND trans,trans- 1,4-DIFLUOROBUTADIENE-1,4-d 2 NORMAN C. CRAIG, YIHUI CHEN, YUHUA LU, CHRISTOPHER F. NEESE, and DEACON J. NEMCHICK, Department of Chemistry and Biochemistry, Oberlin College, Oberlin, OH 44074. THOMAS A. BLAKE, Pacific Northwest National Laboratory, Richland, WA 99252.

2. Goal and Prior Knowledge Semiexperimental (SE) structures for the nonpolar cis,cis and trans,trans isomers of 1,4-difluorobutadiene (DFBD). GS rotational constants for the 2-d 1 isotopologues are known. a GS rotational constants for the singly substituted 13 C and 18 F species can be predicted well from QC calculations. An SE structure for polar cis,trans-DFBD is known from MW spectroscopy. b a Craig, N. C.; Easterday, C. C.; Nemchick, D. J.; Williamson, D. F. K.; Sams, R. L. J. Mol. Spectrosc. 2012, 272, 2. b Demaison, J. F.; Craig, N. C. J. Phys. Chem. A 2011, 115, 8049.

4. cis,cis-DFBD-1-d 1 C-type band for 19

5. Detail of P branch. S/N marginal. Loomis-Wood pattern recognition is essential.

6. Loomis-Wood Display for C-type band ( 19 ) of ccDFBD K a = 9, magenta; 10, red; 11, yellow; 12, green; 13, blue; 14,brown; 15, orange

7. Loomis-Wood Display with only R R 11 highlighted

8. cis,cis-DFBD-1-d 1 C-type band for 20

10. trans,trans-DFBD-1-d 1 C-type band for 18

11. trans,trans-DFBD-1-d 1 C-type band for 21 c for CO 2 w for H 2 O

12. trans,trans-DFBD-1,4-d 2 C-type band for 10

14. Conclusions GS rotational constants have been obtained for the 1-d 1 species of cis,cis and trans,trans-DFBD from the analysis of rotational structure in IR spectra. GS rotational constants for the corresponding 2-d 1 species were found previously. Good GS rotational constants for singly substituted 13 C and 18 F species can be predicted with scaling. The stage is set for determining semiexperimental equilibrium structures of the cis,cis and trans,trans isomers of DFBD.

15. Acknowledgements Peter Groner, University of Missouri at Kansas City Dreyfus Foundation, Senior Scientist Mentor grant. Oberlin College, Department of Chemistry and Biochemistry. Pacific Northwest National Laboratory, Environmental and Molecular Sciences Laboratory.