REACTION PATHWAYS IN THE PHOTOLYSIS OF ACETIC ACID

Abstract

Acetic acid has been photolyzed under both room temperature and jet cooled conditions. The nascent OH $X^{2}\Pi (\nu^{\prime\prime}=0)$ photofragment has been probed using laser fluorescence excitation to determine its scalar and vector quantities. Only a few percent of the total available energy is partitioned into rotational energy of OH. Fragment OH is produced in $\nu=0$ only. The $F_{1}(^{2}\Pi_{3/2})$ and $F_{2}(^{2}\Pi_{1/2})$ spin states are statistically populated, and $\Lambda$-doublet levels are equally populated. The OH product radical was determined to have no rotational alignment. Doppler spectroscopy shows that a significant fraction, about 49%, of the available energy is imparted to $CH_{3}CO$ and OH fragment translation. The energy partitioning shows that the dominant path for OH production from 218 nm acetic acid photolysis is $CH_{3}COOH\to CH_{3}CO + OH$ with no subsequent decomposition of the acetyl fragment. An impulsive model predicts the mean fragment translational energies extracted from the experiments. Alternative pathways that lead to methyl radical fragments will be explored.