The role of an inert gas in the photolysis of acetone

Hoare, D. E.

doi:10.1039/tf9575300791

Cited by 9 publications

(3 citation statements)

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“…Indeed, Hoare has suggested that the extinction coefficient of acetone changes when carbon dioxide is present and that +, , varies with the amount of carbon dioxide added (14,15 (14) but this probably merely reflects differences in the geometry of the two reaction systems or in the methods of filling the cells. Slow mixing was also observed when acetone, or acetone-dG, was mixed with carbon dioxide at 151 "C, but for all three ketones, the observed fractional absorption was independent (+I%,) of the amount of carbon dioxide added, provided that sufficient time was allowed for complete diffusive mixing.…”

Section: Experimental ( I ) P/~oton%cotnpositior~mentioning

confidence: 99%

Primary process in the photolysis of hexafluoroacetone in the presence of mercury vapor

Boyd¹,

Carter²,

Kutschke³

1968

Can. J. Chem.

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Studies have been made of the variation with ketone pressure of the quantum yield for the decomposition of hexafluoroacetone, excited by 3130 A, at 25 and 78 "C, and of the relative yield of the total emission at several temperatures. These are described in considerable detail with a view to discerning possible sources of systematic error. No large systematic error could be identified except that of decreased yields caused by deactivation by mercury vapor. The decomposition data support the weak collision mechanism for vibrational relaxation in the excited singlet state unless an as yet unknown source of large systematic error can be identified.A description is offered of the path of the decomposition in terms of simplified diatomic representations of the nr* singlet and triplet states and of a repulsive state arising from the radicals CF3 and CF3C0 in their ground electronic states. On the basis of that description an activation energy >, 11 kcal mole-1, derived from the combined decomposition and emission data, is to be ascribed to the first-order decomposition of triplet state molecules in vibrational equilibrium with their surroundings.Canadian Journal of Chemistry. 46, 175 (1968) Introduction An earlier publication (1) offered a reinterpretation of literature data as they pertain to the mechanism of the primary process in the photolysis of hexafluoroacetone following excitation by the 3130 group of the mercury arc. The present paper describes in detail the new data cited there, reports additional new data bearing on the primary photodecomposition, and describes a study of some aspects of the emission from the excited states of this ketone. Two brief studies of other aspects of the overall investigation of the primary process have been reported recently (2,3).Near the com~letion of the oresent work the investigations of Bowers and Porter, which are now published (4, 5), came to our attention. There are two important quantitative discrepancies between those results and those reported here. One of these discrepancies can be attributed to the quenching of the triplet state of this ketone by mercury vapor, which was reported recently (3) and since has been confirmed (6, 7). It seems probable that the method used by Bowers and Porter (8) also eliminated a substantial fraction of the mercury from their reactant. Thus their result that 4, -0.2 at room temperature is closer to the unquenched value than that found here (-0.025). The discrepancy (9) regarding the shape of plots of 114 vs. pressure at low pressures cannot be explained as readily.Because of the unexplained discrepailcies the experimental work is described in greater detail here than is usually the case and a discussion is given of possible sources of systematic errors. This description is divided into two sections of which the first describes the experiments on the photodecomposition and the second those on the emission. Experimental ( I ) P/~oton%cotnpositior~The cylindrical quartz photolysis cell (10 crn long, 5 cm diameter) was housed in a cyli...

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Section: Experimental ( I ) P/~oton%cotnpositior~mentioning

confidence: 99%

Primary process in the photolysis of hexafluoroacetone in the presence of mercury vapor

Boyd¹,

Carter²,

Kutschke³

1968

Can. J. Chem.

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“…A number of investigations (Howland & Noyes 1941;Hoare 1957;Caldwell & Hoare 1962) of the effect of added gases, in particular nitrogen and carbon dioxide, have been reported but no studies on the effect of olefines on the primary processes in the gas phase photolysis of acetone appear to have been made. Unique among numerous studies of the reactions of methyl radicals with olefines is the report of Volman & Graven (1953), th a t butadiene appears to depress the decomposition of acetone by an effect which they attributed to the addition of methyl and acetyl radicals to butadiene.…”

Section: Introductionmentioning

confidence: 99%

The mechanism of the gas phase photolysis of acetone

Cundall

Davies

1966

Proc. R. Soc. Lond. A

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A mechanism for the photolysis of acetone has been derived from experimental data including studies on the photosensitized isomerization of olefines. Dissociation into methyl and acetyl radicals occurs from both the first excited singlet and triplet states; the rate constants for excitation by light of 3130 Å wavelength are 2.5 x 10 16 exp ( —16900/ RT ) and 2.5 x 10 10 exp ( — 6400/ RT ) 1. mole -1 s -1 respectively. At low intensities of absorption, decomposition of acetyl radicals predominates over radical-radical interactions. The triplet state is extensively populated at moderate temperatures, the yield at 48 °C being 0.98. The low phosphorescence efficiency of acetone can be ascribed to intersystem crossing to the ground state for which the first order rate constant is 1.25 x 10 5 s -1 . The isomerization data requires the recognition of at least two vibrational levels of the acetone triplet, the rate of electronic energy transfer depending upon the excess energy possessed by the donor

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“…Acetyl radicals so formed are energy rich, and a certain fraction of them are thought to decompose before experiencing any significant number of collisions. The remainder react as acetyl radicals, the predominant reaction being decomposition into carbon monoxide and a methyl radical presumably by a quasi-unimolecular process (6) For personal use only. 9 c o is temperature dependent.…”

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confidence: 99%

PHOTOOXIDATION OF KETONES IN AN O¹⁸ ENRICHED ENVIRONMENT

Dunn¹,

Kutschke²

1958

Can. J. Chem.

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A technique is described in which the origins of the products of photooxidation of ketones call be obtained in respect to whether they arise from the carbonyl or the allcyl groups of the ketone molecule. This is accomplished with the use of reactant molecular oxygen which has been enriched in the 0 ' 8 isotope. Application of this to the photooxidation of acetone indicates that a large fraction of the carbon dioxide contains the carbonyl group of the Icetone and that acetyl radicals play an important role in the oxidation to temperatures a t least a s high as 175" C. Propionyl radicals are much less stable, and, in the photooxidatio~l of diethyl ketone, their reactions, other than decomposition, appear to be negligible a t quite low temperatures. Some cornmelit is made on the mechanisms of these photooxidations.

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The role of an inert gas in the photolysis of acetone

Cited by 9 publications

References 4 publications

Primary process in the photolysis of hexafluoroacetone in the presence of mercury vapor

Primary process in the photolysis of hexafluoroacetone in the presence of mercury vapor

The mechanism of the gas phase photolysis of acetone

PHOTOOXIDATION OF KETONES IN AN O¹⁸ ENRICHED ENVIRONMENT

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The role of an inert gas in the photolysis of acetone

Cited by 9 publications

References 4 publications

Primary process in the photolysis of hexafluoroacetone in the presence of mercury vapor

Primary process in the photolysis of hexafluoroacetone in the presence of mercury vapor

The mechanism of the gas phase photolysis of acetone

PHOTOOXIDATION OF KETONES IN AN O18 ENRICHED ENVIRONMENT

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PHOTOOXIDATION OF KETONES IN AN O¹⁸ ENRICHED ENVIRONMENT