The Structure of Acetaldehyde in its First Excited Singlet State (SI)
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Date
1992
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Publisher
Ohio State University
Abstract
ABSTRACT: High resolution laser induced fluorescence excitation spectra of jet-cooled acetaldehyde and fully deuterated acetaldehyde have been recorded using a pulsed molecular beam apparatus. Analysis of the rotational lines for the vibrationless $S_{1}\Leftarrow S_{0}$ transition has lead to the first experimentally determined structure for the $S_{1}$ excited state of this molecule. Ab initio, self-consistent-field calculations have also been performed as a check on the uniqueness of the fit obtained to the experimental data. In accord with previous predictions, the electronic excitation is found to be an $\pi^{+} \leftarrow n$ C-type perpendicular band, similar to formaldehyde. This results in a loss of planarity in the CCOH group, and an extension of the CO bond length relative to the ground state form. The position of the methyl hydrogens also changes from an eclipsed to a staggered conformation with the CO bond. The excited state rotational constants are found to be: $A^{\prime}=1.596$ $B^{\prime}=0.334$ $C^{\prime}=0.305$. An analysis of the data will be presented.
Description
Author Institution: Department of Chemistry, University of California at Santa Barbara