Reinterpretation of the main absorption band of 1,3-butadiene

Publisher Website
Google Scholar
Abstract
We have measured the near ultraviolet absorption spectrum of 2,3‐dideuterobutadiene to provide a complete set of experimental Bu←X vibrational intervals and bandwidths for all symmetrically deuterated butadienes. These vibrational intervals and bandwidth ratios are compared with the ground state vibrational frequencies and frequency ratios of the molecules. The prominent vibrational frequency interval observed in transitions to the Bu state of butadiene is demonstrated to arise predominantly from a kinetic coupling of the C=C stretching and CH wagging vibrations. The experimental bandwidth ratios are shown to correlate with single quanta of the ground state au CH2 twist frequency interval ratios. From the latter, a plausable decay path for the Bu excited state of butadiene is deduced. The implications of these conclusions on prior and present attempts to determine the butadiene Bu equilibrium geometry and to understand polyene spectroscopy, photochemistry, and photophysics are discussed.