ACETIC ACID DECOMPOSITION DYNAMICS FOLLOWING 1(n,n) EXCITATION
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Date
1990
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Ohio State University
Abstract
Acetic acid has been photolyzed at 200nm at low pressure. The nascent OH $X_{2}\Pi(v^{\prime\prime}= 0)$ photo-fragment has been probed using laser fluorescence excitation to determine its scalar and vector quantities. Only a few percent of the available energy is partitioned into OH rotational energy, and fragment OH is produced in $v^{\prime\prime}=0$ only. The OH A-doublet levels are equally populated, and the $F_{1}(^{2}\Pi_{3/2})$ and $F_{2}(^{2}\Pi_{1/2})$ spin orbit levels are non-statistically populated. The OH fragment is not rotationally aligned. Fragment OH translational energy was determined using Doppler spectroscopy and compared to OH translational energy from acetic acid photolysis at lower energy (218nm) in the same absorption band1. Nearly the same total amount of translational energy is imparted to OH for 200nm and 218nm photolysis, indicating the presence of a barrier to product formation in the decomposition exit channel. Energy partitioning shows that the primary reaction pathway for OH production is $CH_{3}COOH \longrightarrow CH_{3}CO + OH$ for 200 nm acetic acid photolysis. Sufficient energy is channeled into internal energy modes of the acetyl fragment for it to decompose subsequently. RRKM calculations will be presented to indicate whether the acetyl fragment decomposes on the time scale of the experiment. Phase space calculations will also be presented to predict the nascent energy partitioning into the fragments' translational, rotational and vibrational degrees of freedom. Experimental exploration of photochemical reaction mechanisms, such as the formation of an enol intermediate, will also be discussed
Description
$^{1}$ Hunnicutt, S.S.; Waits, L. D.; Guest, J. A. J. Phys. Chem. 1989, 93, 5188-5195.
Author Institution: Department of Chemistry, University of Cincinnati
Author Institution: Department of Chemistry, University of Cincinnati