1. ANALYSIS OF THE ROTATIONAL STRUCTURE IN THE HIGH-RESOLUTION IR SPECTRUM OF trans-HEXATRIENE-3-d 1 NORMAN C. CRAIG and YIHUI CHEN, Department of Chemistry and Biochemistry, Oberlin College, Oberlin, OH, 44074 USA THOMAS A. BLAKE, Physical Science Division, Pacific Northwest National Laboratory, Richland, WA 99352 USA

2. Overall Goal and Progress Overall goal is determining the equilibrium structure of trans-hexatriene. Is there structural evidence for greater π-electron delocalization compared to butadiene? Specifically, are the “C=C” bonds lengthened and is the C(sp 2 )–C(sp 2 ) bond shortened? Compare effects with the isomer, cis-hexatriene. Available GS rotational constants normal, 1,1-d 2, cis-1-d 1, 1- 13 C 1, and 2-d 1 good predictions for 2- 13 C 1 and 3- 13 C 1 Current report – GS rotational constants for tHTE-3-d 1

3. Synthesis

4. Survey IR Spectrum of tHTE-3-d 1 0.1 cm -1 resolution, 22 Torr, 10 cm pathlength

5. Analysis of C-type Band for ν 26 Selection rules: ΔJ = 0, ±1; ΔK a = ±1; ΔK c = 0 Recorded on a Bruker IFS 125HR with 0.0015 cm -1 resolution in a White cell

6. Detail in R Branch of C-type Band for ν 26

7. Overall Structure of ν 28 and ν 29

8. Overall Structure of ν 32

9. Rotational Constants for tHTE-3-d 1 (in cm -1 )

10. Conclusions tHTE-3-d 1 has been synthesized. Rotational structure in four C-type bands has been analyzed. GS rotational constants have been fitted to the combined set of 2234 GSCDs. GS rotational constants for a full set of isotopologues are now available for determining an equilibrium structure of tHTE.

11. Acknowledgments Prof. Albert Matlin suggested the synthesis method, which was explored by Henrik Ehrhardt. Dreyfus Senior Scholar Mentor grant. NSF grant 0420717 for support of a Beowulf supercomputer cluster. Oberlin College. Pacific Northwest National Laboratory.