Thermal Decomposition of CF2Cl2

Kumaran, S. S.; Lim, K. P.; Michael, J. V.; Wagner, Albert F.

doi:10.1021/j100021a036

Cited by 35 publications

(68 citation statements)

References 10 publications

(10 reference statements)

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“…The threshold energy for reaction 1b, where CFCl is in its singlet state, is also ambiguous. Also, if the C-F bond energy in CF 2 Cl, reported by Dispert and Lackman, 20 is combined with ∆ f H°0 ,CF 2 Cl ) 63.0 kcal mol -1 , as suggested from our recent study, 11 then 76.2 kcal mol -1 is obtained in agreement with Ibuki et al 19 A barrier of >8.0 kcal mol -1 has been reported for CF 2 insertion into Cl 2 . For the overall reaction CFCl 3 ) CFCl + 2Cl, Ibuki et al 19 report 133.0 kcal mol -1 , which yields ∆H°0 (1b) ) 75.8 kcal mol -1 .…”

Section: -Eliminationsupporting

confidence: 81%

Thermal Decomposition of CFCl₃

Kumaran

Lim

et al. 1996

J. Phys. Chem.

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The thermal decomposition of CFCl 3 (CFC-11) has been studied in reflected shock waves using the Cl-atom atomic resonance absorption spectroscopy (ARAS) detection technique. The first thermal rate measurements for CFCl 3 (+M) f CFCl 2 + Cl (+M) are reported. The experimental Cl-atom concentration profiles show two distinct rates of formation. The initial fast process gives a Cl-atom yield of 2, and this is followed by slow secondary processes that are density and temperature dependent. The final Cl-atom yield is greater than 2[CFCl 3 ] 0 . This behavior confirms that C-Cl bond scission is the dominant dissociation pathway for both CFCl 3 and the product radical, CFCl 2 , as observed in an earlier study from this laboratory on the related CF 2 Cl 2 decomposition. Profile fits require the fast subsequent dissociation of CFCl 2 , and therefore, the shorttime kinetics can be best explained as being due to C-Cl bond breaking in the parent, CFCl 3 . The temperature and density dependences of the later time Cl-atom profiles suggest that the slow secondary rate can be ascribed to reactions involving the carbene diradical, CFCl. The Cl-atom data were analyzed with detailed kinetics modeling calculations. Experiments were performed with varying [CFCl 3 ] 0 (15. 23, 7.877, 5.159, and 2.496 ppm) in Kr diluent at three (3.1 × 10 18 , 2.1 × 10 18 , and 1.2 × 10 18 cm -3 ) post-shock densities. An Arrhenius fit to the experimental CFCl 3 dissociation rates over the T-range 1279-1950 K gives k ) (2.82 ( 1.22) × 10 -8 exp(-26420 ( 674 K/T) cm 3 molecule -1 s -1 , with (36% error at the one standard deviation level. Comparing this expression to earlier results from this laboratory on CF 3 Cl, CF 2 Cl 2 , and CCl 4 suggests that the C-Cl bond strength in CFCl 3 should be between those for CF 2 Cl 2 and CCl 4 . The temperature and pressure dependence of the rate constants, i.e., the falloff from the low-pressure limit, have been characterized with Rice-Ramsperger-Kassel-Marcus (RRKM) calculations using E 0 ) (76.5 ( 0.5) kcal mol -1 with 〈∆E〉 down ) (800 ( 215) cm -1 . This E 0 implies ∆ f H°0 ,CFCl 2 ) -20.3 kcal mol -1 , and subsequently ∆H°0 ) (58 ( 2) kcal mol -1 for CFCl 2 f CFCl

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Section: -Eliminationsupporting

confidence: 81%

Thermal Decomposition of CFCl₃

Kumaran

Lim

et al. 1996

J. Phys. Chem.

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“…25 Although they concluded that Cl2 was not formed, their result is not necessarily at odds with the present work since at higher energies, the isomer will decay to both radical and molecular products (Figure 1), which lowers the yield of the molecular channel. To illustrate, we extended our RRKM calculations to an energy corresponding to the threshold for secondary dissociation of CF2Cl and included a second step to model the decay of the isomer, which would be born with ∼60 kcal/mol of energy.…”

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confidence: 60%

“…25 Although they concluded that Cl2 was not formed, their result is not necessarily at odds with the present work since NOT THE PUBLISHED VERSION; this is the author's final, peer-reviewed manuscript. The published version may be accessed by following the link in the citation at the bottom of the page.…”

Section: Journal Of Physical Chemistrymentioning

confidence: 51%

Isomerization as a Key Path to Molecular Products in the Gas-Phase Decomposition of Halons

Kalume

George

Reid

2010

J. Phys. Chem. Lett.

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NOT THE PUBLISHED VERSION; this is the author's final, peer-reviewed manuscript. The published version may be accessed by following the link in the citation at the bottom of the page. Letters, Vol. 1, No. 20 (2010): pg. 3090-3095. DOI. This article is © American Chemical Society and permission has been granted for this version to appear in e-Publications@Marquette. American Chemical Society does not grant permission for this article to be further copied/distributed or hosted elsewhere without the express permission from American Chemical Society. Journal of Physical Chemistry 2The decomposition of halons remains controversial concerning the branching between radical and molecular products. The latter channel, where it has been found, is presumed to occur via a constrained symmetric multicenter transition state. Isomerization pathways in the gas-phase chemistry of halons have rarely been considered, despite the fact that the iso-halons, which feature a halogen−halogen bond, are widely recognized as important reactive intermediates in condensed phases. In this Letter, detailed calculations and modeling of the unimolecular decomposition of several important halons, including CF2Cl2, CF2Br2, and CHBr3, reveal that isomerization is a key pathway to molecular products. This path is important for both halons and their primary radicals as the barrier to isomerization in these compounds is typically isoenergetic with the threshold for bond fission. Keywords: decomposition; halocarbons; iso-halomethanes; isomerization Halocarbons such as chlorofluorocarbons (CFCs) are famous for their role in ozone depletion, 1 and due to their past widespread industrial use, it is crucial to understand the pathways for their decomposition. Perhaps surprisingly, the decomposition of simple halons such as CF2Cl2, CF2Br2, and CHBr3 remains controversial concerning the branching between radical and molecular products. The latter channel, where it has been found, is usually assumed to involve a constrained symmetric multicenter transition state, which has not been identified computationally. 2 The iso-halons are well-known condensed-phase reactive intermediates that possess a halogen−halogen bond; 3-15 yet, few studies have suggested a role for these species in the gas-phase chemistry of halons. In recent studies of the multiphoton dissociation of the halons CHX3 and CX4, (X = Br,I), Quandt and coworkers suggested on the basis of secondary evidence a mechanism that involved the isospecies. 16,17 However, to date, conclusive evidence has not been provided for the role of isomerization in the thermal or photoinitiated decomposition of halons.Our interest in this topic began in recent studies of the spectroscopy and photochemistry of the weakly bound iso-CF2X2 (X = Br, I) species, which were trapped in Ar and Ne matrixes at 5 K. 18,19 Excitation into the intense near-UV band of iso-CF2Br2 resulted in back-isomerization to CF2Br2, 19 and intrinsic reaction coordinate (IRC) calculations showed that a first-order saddle point connects th...

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“…[ls], CH3Cl [10,11], C3H3Cl [19], CFC13 [16,20], CF2C12 [16,21], CF3Cl [16,22], CF2HCl [13], CF3I [12], CH3I [23], C2H5I [24], C6H5I [25], and CC120 [26]. The methods used are nearly identical in all cases, and for the purposes of discussion, we will illustrate the method with CH3I data -ln(IdIo) (It and Io refer to transmitted and incident I-atom resonance light intensities, respectively), is measured as CH3I decomposes.…”

Section: Resultsmentioning

confidence: 99%

Thermal Decomposition Studies of Halogenated Organic Compounds

Michael¹,

Kumaran²

1998

Combustion Science and Technology

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Thermal Decomposition of CF2Cl2

Cited by 35 publications

References 10 publications

Thermal Decomposition of CFCl₃

Thermal Decomposition of CFCl₃

Isomerization as a Key Path to Molecular Products in the Gas-Phase Decomposition of Halons

Thermal Decomposition Studies of Halogenated Organic Compounds

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Thermal Decomposition of CF2Cl2

Cited by 35 publications

References 10 publications

Thermal Decomposition of CFCl3

Thermal Decomposition of CFCl3

Isomerization as a Key Path to Molecular Products in the Gas-Phase Decomposition of Halons

Thermal Decomposition Studies of Halogenated Organic Compounds

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Thermal Decomposition of CFCl₃

Thermal Decomposition of CFCl₃