THE PUZZLING MICROWAVE SPECTRUM OF HEXADIENAL
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Date
1985
Journal Title
Journal ISSN
Volume Title
Publisher
Ohio State University
Abstract
The microwave spectrum of trans, trans-2, 4-hexadienal can be assigned to the species with anti-periplanar conformations about the C-C single bonds (1). Hexadienal is a nearly symmetric top ($kappa = -0.997$, calc’d) whose a-type R-branch pileups form narrow (5 MHz FWHM) bands whose K components are unresolved but the bands from each vibrational species are resolved from each other. The spectrum reveals a complex array of vibrational satellite bands extending upward in frequency from the ground state band (B+C = 1592.5 MHz). Assuming the torsional modes about the two central C-C single bonds are the molecule’s lowest frequency vibrational modes, that torsional potential functions from acrolein and butadiene are transferable to hexadienal, and that the operator for B+C is represented by the geometrically calculated B+C as a function of the two torsional angles, much of the vibrational satellite structure of the spectrum can be simulated. This model describes the microwave spectrum with one glaring deficiency: the intense, broad absorption bands displaced to slightly higher frequencies (B+C = 1604.0 MHz) from the ground state and the discrete vibrationally excited species are not explained. Various models for this intense band series will be discussed.
Description
(1) W. E. Steinmetz, J. E. Pollard, J. M. Blaney, B. K. Winker, I. K. Mun, F. J. Hickernell and S. J. Hollenberg, J. Phys. Chem. 83, 1540 (1979).
Author Institution: Department of Chemistry, University of Connecticut; Department of Chemistry, University of Connecticut; Department of Chemistry, University of Connecticut
Author Institution: Department of Chemistry, University of Connecticut; Department of Chemistry, University of Connecticut; Department of Chemistry, University of Connecticut