15min:

NORMAN C. CRAIG, KEITH A. HANSON AND MICHAEL C. MOORE, Department of Chemistry, Oberlin College, Oberlin, OH 44074; ROBERT L. SAMS, Pacific Northwest National Laboratory, P.O. Box 999, Mail Stop K8-88, Richland, WA 99352.

Considerable progress has been made toward obtaining ground state rotational constants for butadiene (BDE) and its isotopomers for use in fitting an equilibrium structure. With the exception of a microwave investigation of the weakly polar BDE-1,1- d ₂, studies of all of the other, nonpolar species have been done with high-resolution (0.002 cm^-1) infrared spectroscopy. Rotational constants are available for BDE and BDE-2,3- d ₂ from one study and for the three species of BDE-1,4- d ₂ from another study. The present report is on BDE-1-¹³ C ₁. The rotational structure in the C-type bands at 524 cm^-1, 900 cm^-1, and 908 cm^-1 in the infrared spectrum has been analyzed. Rotational constants fit to 2191 ground state combination differences derived from all three bands are (in cm^-1) A = 1.3887919 (6), B = 0.1436683 (3), and C = 0.1302251 (3). In the parent molecule of C _2h symmetry, a Raman-active b _g mode occurs at 908 cm^-1 and an infrared-active mode occurs at essentially the same frequency. In BDE-1-¹³ C ₁ of reduced, C _s symmetry, both modes have significant infrared intensity and occur at 908 and 900 cm^-1. The higher frequency mode is CH₂ flapping; the lower frequency one is ¹³CH₂ flapping. \footnoteP.~Huber-Wälchli and Hs.~H.~Günthard Spectrochim. Acta , \textbf37A, 285, (1981); Yu.~N.~Panchenko, private communication.