Analysis of rotational structure in the high-resolution infrared spectrum and assignment of vibrational fundamentals of butadiene-2,3- 13C 2

Abstract

The 2,3- 13C 2 isotopomer of butadiene was synthesized, and its fundamental vibrational fundamentals were assigned from a study of its infrared and Raman spectra aided with quantum chemical predictions of frequencies, intensities, and Raman depolarization ratios. For two C-type bands in the high-resolution (0.002 cm −1) infrared spectrum, the rotational structure was analyzed. These bands are for ν 11 ( a u ) at 907.17 cm −1 and for ν 12 ( a u ) at 523.37 cm −1. Ground state and upper state rotational constants were fitted to Watson-type Hamiltonians with a full quartic set of centrifugal distortion constants and two sextic ones. For the ground state, A 0 = 1.3545088(7) cm −1, B 0 = 0.1469404(1) cm −1, and C 0 = 0.1325838(2) cm −1. The small inertial defects of butadiene and two 13C 2 isotopomers, as well as for five deuterium isotopomers as previously reported, confirm the planarity of the s-trans rotamer of butadiene.