Atomic and Free Radical Reactions.

Steacie, E. W. R.; Livingston, Robert

doi:10.1021/j150449a010

Cited by 149 publications

(78 citation statements)

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“…It is well known [21] that ethylene is not a product in systems where methyl radicals are the major intermediate reactants.…”

Section: The Formation Of Ethylene and Acetylene Productsmentioning

confidence: 99%

“…Of this, 60 percent can be accounted for by the elimination of reaction (4) (as evidenced by the drop in the acetylene yield). Thus, the maximum yield which could be attributed to process (21) or (23) (23), we can say that the maximum yield which could be attributed to this process would be the difference between the hydrogen yield in the low dose rate radiolysis [22] of a CH4 -NO mixture (0.95) where neutralization processes do not contribute, and that observed in the pulse radiolysis in the presence of SF6 (1.16), a difference of 0.21. By elimination, then, we write as the most probable neutralization reaction of CHt, process (5), the forma· tion of an H atom and a methane molecule.…”

mentioning

confidence: 99%

“…CHt neutralization results in the formation of CHz radicals: (21) The occurrence of this reaction to give three H atoms as products can be excluded on energetic grounds; this process would be 25 kcal/mol endothermic.…”

mentioning

confidence: 99%

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Pulse radiolysis of methane

Rebbert¹,

Lias²,

Ausloos³

1973

J. RES. NATL. BUR. STAN. SECT. A.

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The pulse radiolysis of methane has been studied in the absence and presence of electron scaven· gers such as SFs and C03I and positive ion scavengers such as i-C,O,o in order to define the role of the intermediates H, C, CH, CH2, CR" C H~, and C,H~ in product formation. The dose rate was varied from 0.68 to 15.2 X 10'9 eV/g-s, the dose (number of pulses) was varied, and th e duration of the pulse was c hanged from 3 ns to 100 ns. The variation of the yields of th e ethylene and ethan e products with dose is explained by the reaction of H-atoms with accumulated ethylene product. The fast reacting C, CH, and 'CH2 species insert into methane to form acetylene, ethylene , and ethane products, but a ll of the reaction s of these species cannot be completely specified since they may originate in upper electronic states, whose reactions with methane are unknown. Product formation by the slow reacting 3CH2 and CH3 radicals is also examined; for instance, evidence is presented for the occurrence of the rea ction:"C H2 + CH3 --> C2 H, + H. Results indi cate that the ion s 'CHt and C,H ~ undergo neutralization mainly throu gh the processes CHt+e--> CH.+ H C2 H; + e --> (C, H,) ' + H --> C,H2 + H + H2 (2H).When i-C,Ow is added, a fra ction of the CH; and C2H; react with th e ad ditive rather than undergo neutralization. A calcu lation demonstrates that the fraction of ions undergoing reaction with a given concentration of i-C,D,o can be correctly predi cted by assuming that th e rate constant for neutralization of CH; and C2H; is the same as that ':!etermined recently for th e t-butyl ion.

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“…It is well known [21] that ethylene is not a product in systems where methyl radicals are the major intermediate reactants.…”

Section: The Formation Of Ethylene and Acetylene Productsmentioning

confidence: 99%

mentioning

confidence: 99%

See 1 more Smart Citation

Pulse radiolysis of methane

Rebbert¹,

Lias²,

Ausloos³

1973

J. RES. NATL. BUR. STAN. SECT. A.

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“…4 indicate the presence of more than one precursor of hydrogen reacting with carbon tetrachloride. We identify these precursors as the electron and the hydrogen atom, in view of their known reactions with carbon tetrachloride in the vapor phase (6,29).…”

Section: Discussionmentioning

confidence: 99%

The X-radiolysis of water vapor containing methanol. Effects of some electron and hydrogen atom scavengers

Dixon¹,

Bailey²

1968

Can. J. Chem.

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“…Therefore, insofar as radiation heating of the propellant has a significant influence on the design of a nuclear-powered vehicle, further calculations of the rates of radiation-induced molecular reactions are warranted; and any experimental data obtained on the radiation heating of liquid hydrogen should be interpreted in the light of possible delays in the equipartition of energy stored in radiation products. 2,4,12,14,18,46,60,98,112,124,130. …”

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confidence: 99%

Energy Storage Mechanisms in Liquid Hydrogen

Carter¹

1962

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Energy-storing molecular products of radiation in liquid hydrogen are examined from the point of view that the explusion of potential energy in the form of such products may lead to lower design weights for nuclear rockets. It is found that a significant fraction of the energy deposited by radiation in liquid hydrogen is stored temporarily through the dissociation and excitation of H2 molecules" Experimental and theoretical results are consistent with a rate of dissipation of such energy into thermal motion which is much slower than the rate at which the radiation products are expelled from the tank. It is shown that, if this is the case, relatively high levels of infrared radiation are to be expected but that such energy will not rapidly be translated into thermal motion. It is concluded that, insofar as radiation heating of the propellant is a significant design factor, further consideration should be given to radiation-induced reactions in liquid hydrogen and that any radiation-heating experiments should be interpreted in terms of possible energy-storage effects" 3 Blank page REPORT SUMMARY Hydrogen-propelled nuclear vehicles play a leading role in presently envisaged space missions. Therefore, the processes associated with radiation-heating in liquid hydrogen are worthy of attention. Of particular interest from the standpoint of propellantshield design is the formation of energy•=»storing molecular species through which the production of actual thermal energy is temporarily postponed. Consideration of potential energy expelled from the system in the form of such species may lead to lower overall design weights, owing to less stringent provisions for shielding, pressurevessel construction, and/or boil-off" The object of the present study is to determine whether an appreciable amount of the energy deposited by radiation is stored in radiation products and whether such products survive in the liquid long enough to be expelled from the system. In realistic cases most of the radiation products are formed near the exit, and the time required for their expulsion is only about 20 seconds.Energy deposited in liquid hydrogen by neutral radiation is initially transferred to recoil protons or Compton-scattered electrons in the case of neutrons or gamma rays, respectively.When such charged particle pass through the hydrogen, which is normally almost entirely in the H2 ground state, approximately equal amounts of energy go into the production of H-atom pairs.5 through the formation of the repulsive •^s^ H2 state and into the production of Hg ions. By means of reactions such as HJ + H2=^'H+ -h H : H^ -f e" =^H* + H, the ionization process leads indirectly to further dissociation and excitation. Through ionic ajid dissociative reactions alone, about 43^ of the energy deposited is temporarily stored in the production of H atoms and excited Hg molecules. Most of the remaining energy is initially released by the ejection of H atoms from repulsive molecular configurations. The total amount of energy storage could be sub...

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Atomic and Free Radical Reactions.

Cited by 149 publications

References 0 publications

Pulse radiolysis of methane

Pulse radiolysis of methane

The X-radiolysis of water vapor containing methanol. Effects of some electron and hydrogen atom scavengers

Energy Storage Mechanisms in Liquid Hydrogen

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