Fragmentation Pathways in a Series of CH<sub>3</sub>COX Molecules in the Strong Field Regime

Anand, Smriti; Zamari, Muhannad M.; Menkir, Getahun; Levis, Robert J.; Schlegel, H. Bernhard

doi:10.1021/jp0372789

Cited by 18 publications

(15 citation statements)

References 22 publications

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“…Paltenghi et al 25 have suggested that the reactivity of alkyl radicals with Cl 2 is determined largely by long‐range attractive forces, and a correlation of the rate coefficient for barrierless reactions with the reactant molecules ionization potential (IP) has been proposed. The IP values for HCO 26 and CF 3 CO 27 are 8.6 eV and that for CH 3 CO is 7 eV 26. Hence, the rate coefficient for the Cl 2 + CH 3 CO reaction is expected to be greater than the analogous HCO and CF 3 CO reactions.…”

Section: Discussionmentioning

confidence: 91%

Rate coefficients for the reaction of the acetyl radical, CH₃CO, with Cl₂ between 253 and 384 K

Gierczak

Rajakumar

Flad

et al. 2009

Int J of Chemical Kinetics

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Rate coefficients, k, for the gas-phase reaction CH 3 CO + Cl 2 → products (2) were measured between 253 and 384 K at 55-200 Torr (He). Rate coefficients were measured under pseudo-first-order conditions in CH 3 CO with CH 3 CO produced by the 248-nm pulsedlaser photolysis of acetone, CH 3 C(O)CH 3 , or 2,3-butadione, CH 3 C(O)C(O)CH 3 . The loss of CH 3 CO was monitored by cavity ring-down spectroscopy (CRDS) at 532 nm. Rate coefficients were determined by first-order kinetic analysis of the CH 3 CO temporal profiles for [Cl 2 ] < 1 × 10 14 molecule cm −3 and the analysis of the CRDS profiles by the simultaneous kinetics and ring-down method for experiments performed with [Cl 2 ] > 1 × 10 14 molecule cm −3 . k 2 (T ) was found to be independent of pressure, with k 2 (296 K) = (3.0 ± 0.5) × 10 −11 cm 3 molecule −1 s −1 . k 2 (T ) showed a weak negative temperature dependence that is well reproduced by the Arrhenius expression k 2 (T ) = (2.2 ± 0.8) × 10 −11 exp[(85 ± 120)/T ] cm 3 molecule −1 s −1 . The quoted uncertainties in k 2 (T ) are at the 2σ level (95% confidence interval) and include estimated systematic errors. A comparison of the present work with previously reported rate coefficients for the CH 3 CO + Cl 2 reaction is presented. C

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Section: Discussionmentioning

confidence: 91%

Rate coefficients for the reaction of the acetyl radical, CH₃CO, with Cl₂ between 253 and 384 K

Gierczak

Rajakumar

Flad

et al. 2009

Int J of Chemical Kinetics

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“…The other radical cleavage products, phenyl and acetyl radicals, are also observed but with a much lower yield. 45,52,53 Like benzaldehyde, the yield of chemical products is seen to approach unity with S 2 excitation at the lowest pressures but decreases coincident with increasing phosphorescence when foreign gas is added, suggesting a vibrationally excited intermediate to fragmentation. Only trace amounts of the molecular dissociation products of carbon monoxide and toluene were detected after photolysis by 193 and 248 nm radiations; a branching ratio with the radical products of ϳ1 : 100.…”

Section: B Acetophenonementioning

confidence: 99%

Ultrafast electron diffraction: Excited state structures and chemistries of aromatic carbonyls

Park

Feenstra

Zewail

2006

The Journal of Chemical Physics

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The photophysics and photochemistry of molecules with complex electronic structures, such as aromatic carbonyls, involve dark structures of radiationless processes. With ultrafast electron diffraction ͑UED͒ of isolated molecular beams it is possible to determine these transient structures, and in this contribution we examine the nature of structural dynamics in two systems, benzaldehyde and acetophenone. Both molecules are seen to undergo a bifurcation upon excitation ͑S 2 ͒. Following femtosecond conversion to S 1 , the bifurcation leads to the formation of molecular dissociation products, benzene and carbon monoxide for benzaldehyde, and benzoyl and methyl radicals for acetophenone, as well as intersystem crossing to the triplet state in both cases. The structure of the triplet state was determined to be "quinoidlike" of * character with the excitation being localized in the phenyl ring. For the chemical channels, the product structures were also determined. The difference in photochemistry between the two species is discussed with respect to the change in large amplitude motion caused by the added methyl group in acetophenone. This discussion is also expanded to compare these results with the prototypical aliphatic carbonyl compounds, acetaldehyde and acetone. From these studies of structural dynamics, experimental and theoretical, we provide a landscape picture for, and the structures involved in, the radiationless pathways which determine the fate of molecules following excitation. For completeness, the UED methodology and the theoretical framework for structure determination are described in this full account of an earlier communication ͓J. S. Feenstra et al., J. Chem. Phys. 123, 221104 ͑2005͔͒.

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“…[11][12][13] Both molecules have been observed to dissociate upon UV irradiation: benzaldehyde along a molecular dissociation pathway leading to closed-shell species, benzene and carbon monoxide, [14][15][16][17][18][19][20][21] and acetophenone into radical products, benzoyl and methyl radicals. 16,[22][23][24] Minor radical production pathways have also been detected from benzaldehyde. 25,26 In the condensed phase, photophysical studies of benzaldehyde 5 and acetophenone 6 ͑in matrices͒ and benzaldehyde derivatives 27 ͑in solution͒ indicate that the triplet ͑T 2 ͒ state becomes the lowest in energy and hence identifiable by its emission.…”

Section: Introductionmentioning

confidence: 99%

Excited state molecular structures and reactions directly determined by ultrafast electron diffraction

Feenstra

Park

Zewail

2005

The Journal of Chemical Physics

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In this communication, we report on the use of ultrafast electron diffraction to determine structural dynamics of excited states and reaction products of isolated aromatic carbonyls, acetophenone and benzaldehyde. For a 266nm excitation, a bifurcation of pathways is structurally resolved, one leading to the formation of the triplet state (quinoid structure) and another to chemical products: for benzaldehyde the products are benzene and carbon monoxide (hydrogen migration and bond rupture) while those for acetophenone are the benzoyl and methyl radicals (bond rupture). The refined structures are compared with those predicted by theory. These dark structures and their radiationless transitions define the reduced energy landscape for complex reactions.

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Fragmentation Pathways in a Series of CH₃COX Molecules in the Strong Field Regime

Cited by 18 publications

References 22 publications

Rate coefficients for the reaction of the acetyl radical, CH₃CO, with Cl₂ between 253 and 384 K

Rate coefficients for the reaction of the acetyl radical, CH₃CO, with Cl₂ between 253 and 384 K

Ultrafast electron diffraction: Excited state structures and chemistries of aromatic carbonyls

Excited state molecular structures and reactions directly determined by ultrafast electron diffraction

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Fragmentation Pathways in a Series of CH3COX Molecules in the Strong Field Regime

Cited by 18 publications

References 22 publications

Rate coefficients for the reaction of the acetyl radical, CH3CO, with Cl2 between 253 and 384 K

Rate coefficients for the reaction of the acetyl radical, CH3CO, with Cl2 between 253 and 384 K

Ultrafast electron diffraction: Excited state structures and chemistries of aromatic carbonyls

Excited state molecular structures and reactions directly determined by ultrafast electron diffraction

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Product

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Fragmentation Pathways in a Series of CH₃COX Molecules in the Strong Field Regime

Rate coefficients for the reaction of the acetyl radical, CH₃CO, with Cl₂ between 253 and 384 K

Rate coefficients for the reaction of the acetyl radical, CH₃CO, with Cl₂ between 253 and 384 K