Evidence for stepwise dissociation dynamics in acetone at 248 and 193 nm
- Chemical Sciences Division, Lawrence Berkeley Laboratory and Department of Chemistry, University of California, Berkeley, California 94720 (United States)
The technique of molecular beam photofragment translational spectroscopy has been used to study the dissociation of acetone following [ital S][sub 1][l arrow][ital S][sub 0] (248 nm) and [ital S][sub 2][l arrow][ital S][sub 0] (193 nm) excitation. Excitation at 248 nm resulted in the production of CH[sub 3] and CH[sub 3]CO with 14.2[plus minus]1.0 kcal/mole on average of the available energy appearing as translation of the photofragments. Comparison of the measured [l angle][ital E][sub [ital T]][r angle] with values reported at 266 nm suggest that the energy partitioning is dominated by the exit barrier caused by an avoided crossing on the potential energy surface. A substantial fraction (30[plus minus]4%) of the nascent acetyl radicals from the primary dissociation contain sufficient energy to undergo spontaneous secondary decomposition. From the onset of the truncation of the CH[sub 3]CO [ital P]([ital E][sub [ital T]]) a threshold of 17.8[plus minus]3.0 kcal/mole for the dissociation of the acetyl radical has been determined in agreement with recent results on the photodissociation of acetyl chloride. The translational energy release in the dissociation of CH[sub 3]CO closely matches the experimentally determined exit barrier. At 193 nm the only observed dissociation pathway was the formation of two methyl radicals and carbon monoxide. On average [similar to]38% of the available energy is found in product translation suggesting that significant internal energy resides in the nascent CH[sub 3] fragments consistent with the results of Hall [ital et] [ital al]. [J. Chem. Phys. [bold 94], 4182 (1991)]. We conclude that the dynamics and energy partitioning for dissociation at 193 nm is similar to that at 248 nm. [copyright] [ital 1995] [ital American] [ital Institute] [ital of] [ital Physics].
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 6455257
- Journal Information:
- Journal of Chemical Physics; (United States), Vol. 102:11; ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ACETONE
PHOTOLYSIS
CARBONYL RADICALS
YIELDS
METHYL RADICALS
ACETYL RADICALS
MOLECULAR BEAMS
SPECTROSCOPY
ULTRAVIOLET RADIATION
ACYL RADICALS
ALKYL RADICALS
BEAMS
CHEMICAL REACTIONS
DECOMPOSITION
ELECTROMAGNETIC RADIATION
KETONES
ORGANIC COMPOUNDS
PHOTOCHEMICAL REACTIONS
RADIATIONS
RADICALS
400500* - Photochemistry