Photofragmentation of ketene to CH sub 2 ( tilde X sup 3 B sub 1 ) + CO. 1. Barrier height and dissociation rate constant

Journal Article · Thu Jan 11 04:00:00 EST 1990 · Journal of Physical Chemistry; (USA)

DOI:https://doi.org/10.1021/j100364a043· OSTI ID:6730267

Chen, Ichia; Moore, C B ^[1]

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1. Lawrence Berkeley Lab., CA (USA)

Ketene cooled in a supersonic free jet is photolyzed in the ultraviolet range. The appearance rate of fragment CO from triplet ketene as a function of ultraviolet photon energy is measured by vacuum-ultraviolet laser-induced fluorescence. A tunneling-corrected RRKM theory is used to fit the observed dissociation rate of ketene using the ab initio vibrational frequencies of the transition state. The density of states inferred from the RRKM fit is a factor of 2 greater than the density of states of the ground electronic state (S{sub 0}) and 300 times greater than that of T{sub 1}. Tunneling corrections are necessary to fit the dissociation rate below the top of the exit barrier. The experimental rates show a sharp change in slope at 28,290-cm{sup {minus}1} photolysis frequency. The height of the exit barrier is determined to be 3.79 {plus minus} 0.06 kcal/mol above ground-state fragments. The imaginary frequency that fits the data is (150 {plus minus} 25)i cm{sup {minus}1}, much lower than the ab initio frequency of 523i cm{sup {minus}1}. At higher energies the RRKM theory predicts faster rates than are observed. It is possible that the intersystem crossing rate is relatively independent of energy and becomes the rate-determining step for formation of triplet products at higher energies.

• DOE Contract Number: AC03-76SF00098
• OSTI ID: 6730267
• Journal Information: Journal of Physical Chemistry; (USA), Journal Name: Journal of Physical Chemistry; (USA) Vol. 94:1; ISSN 0022-3654; ISSN JPCHA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
400500 -- Photochemistry
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CHALCOGENIDES
CHEMICAL REACTIONS
DATA
DATA ANALYSIS
DECOMPOSITION
DISSOCIATION
EMISSION SPECTROSCOPY
EXPERIMENTAL DATA
FLUORESCENCE SPECTROSCOPY
INFORMATION
KETENES
KINETICS
MEASURING INSTRUMENTS
MEASURING METHODS
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
PHOTOLYSIS
SPECTROSCOPY
THEORETICAL DATA