ANALYSIS OF ROTATIONAL STRUCTURE IN THE HIGH-RESOLUTION INFRARED SPECTRUM OF {\em cis}-1,3,5-HEXATRIENE

Abstract

Author Institution: Department of Chemistry and Biochemistry, Oberlin College, Oberlin, OH 44074; Environmental and Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99352The high-resolution infrared spectrum has been recorded for two C-type bands of {\em cis}-1,3,5-hexatriene. The resolution (0.0013 cm$^{-1}$) and the Doppler width (0.0012 cm$^{-1}$ at 900 cm$^{-1}$) are barely adequate for observing detailed rotational structure of this heavy molecule in a spectrum recorded at room temperature. An additional complication is the extensive hot band structure arising from excited states of the low frequency C-C torsional modes. A preliminary analysis of rotational structure yielded $^{R}$$R$$_{K}$ and $^{P}$$P$$_{K}$ series in each of the two bands, centered at 908 cm$^{-1}$ and 586 cm$^{-1}$. However, ground state combination differences (GSCDs) failed to fit a rotational Hamiltonian. Subsequent microwave spectroscopic measurements gave ground state rotational constants. Reliable GSCDs computed from the ground state rotational constants led to revisions in assignments of some of the sub-band series in the infrared spectrum and to a convincing assignment