10min:

NORMAN C. CRAIG AND MATTHEW C. LEYDEN, Department of Chemistry and Biochemistry, Oberlin College, Oberlin, OH 44074; TONY MASIELLO, Environmental and Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99352.

The high-resolution infrared spectrum has been recorded for two C-type bands of 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 ^RR_K and ^PP_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.