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

1968 ◽  
Vol 46 (12) ◽  
pp. 1957-1964 ◽  
Author(s):  
R. S. Dixon ◽  
M. G. Bailey
Keyword(s):  
Nitrous Oxide ◽  
Water Vapor ◽  
Carbon Tetrachloride ◽  
Hydrogen Atom ◽  
Sulfur Hexafluoride ◽  
Hydrogen Yield ◽  
Hydrogen Atoms ◽  
A Value ◽  
Ion Recombination ◽  
Positive Ion

The X-radiolysis of water vapor containing methanol at 125 °C and 1 atm pressure has been studied alone and in the presence of some electron and hydrogen atom scavengers. In water vapor containing methanol only, a plateau value G(H2) = 7.9 ± 0.3 is obtained at all methanol concentrations above 0.5 mole %. Addition of propylene drastically reduces this yield due to efficient scavenging of hydrogen atoms, and values for the total number of H atoms from all precursors g(H)t = 7,5 ± 0.2 and [Formula: see text] are deduced from the competition. An unscavengeable hydrogen yield g(H2) ~ 0.5 is also indicated in mixtures containing propylene. Nitrous oxide and sulfur hexafluoride are found to scavenge electrons efficiently in water vapor containing methanol and the number of hydrogen atoms arising from electron–positive ion recombination is estimated to have a value G = 2.2 ± 0.6. The number of hydrogen atoms arising from processes not involving electrons is g(H) = 5.2 ± 0.3. Carbon tetrachloride reacts efficiently with both electrons and hydrogen atoms, with k(H + CH3OH)/k(H + CCl4) = 0.085. Values of g(H) = 4.9 ± 0.5 and g(H2) = 0.8 ± 0.2 are deduced from mixtures containing carbon tetrachloride.

RADIATION CHEMISTRY OF CYCLOHEXANE: VI. DILUTE SOLUTIONS OF CARBON TETRACHLORIDE AND CHLOROFORM IN CYCLOHEXANE

1964 ◽  
Vol 42 (3) ◽  
pp. 669-681 ◽  
Author(s):  
J. A. Stone ◽  
P. J. Dyne
Keyword(s):  
Carbon Tetrachloride ◽  
Chemical Reaction ◽  
Physical Process ◽  
Radical Scavenging ◽  
Radiation Chemistry ◽  
Hydrogen Yield ◽  
Halogenated Compounds ◽  
Dilute Solutions ◽  
Hydrogen Atoms

A study of the effect of the addition of small amounts (<3.5%) of the halogenated compounds CCl4, CHCl3, and CDCl3 on the radiolysis of cyclohexane has shown that processes other than radical scavenging occur. At the lowest concentrations of solute that it was practical to employ (0.004 M) cyclohexyl radicals were scavenged without a corresponding reduction in the hydrogen yield. At higher solute concentrations G(H2) was reduced by a physical process which did not involve the scavenging of thermal hydrogen atoms but did lead to chemical reaction involving the solute.

Effect of Pressure on the Rates of Reaction of Radiolysis Intermediates in Liquid n-Hexane

1971 ◽  
Vol 49 (16) ◽  
pp. 2651-2656 ◽  
Author(s):  
Kamal N. Jha ◽  
Gordon R. Freeman
Keyword(s):  
Carbon Tetrachloride ◽  
Hydrogen Atom ◽  
Pressure Dependence ◽  
Diffusion Coefficients ◽  
Effect Of Pressure ◽  
Scavenging Efficiency ◽  
Kinetics Of ◽  
Positive Ion

The yield of hydrogen from pure hexane, G(H2) = 5.3 ± 0.2 was independent of pressure in the range 1 bar to 4.6 kbars. The G values of H2, HD, and D2 obtained from 11 mol% C6D14 in C6H14 were independent of pressure and were respectively, 4.85, 0.34, and 0.11. The electron and hydrogen atom scavenging efficiencies of carbon tetrachloride and hexadiene-1,3, and the hydrogen atom scavenging efficiency of hexene-1 were independent of pressure. The positive ion scavenging efficiencies of benzene and aniline increased with increasing pressure. The volume of activation for the hydrogen atom reaction with n-hexane is essentially the same as that for the reaction with hexene-1. The pressure dependence of the charge scavenging reactions has been interpreted in terms of the kinetics of spur processes. The treatment is consistent with the fact that the efficiency of the electron scavenging reactions is independent of pressure. The increased efficiency of positive ion reaction under pressure implies that the ratio of the diffusion coefficients of the radiolytic positive ion and electron, D+/D−, increases with increasing pressure.

Effects of electron scavengers in the radiolysis of water vapor

1968 ◽  
Vol 46 (8) ◽  
pp. 1181-1186 ◽  
Author(s):  
R. S. Dixon ◽  
M. G. Bailey
Keyword(s):  
Nitrous Oxide ◽  
Water Vapor ◽  
Cross Sections ◽  
Electron Attachment ◽  
Hydrogen Yield ◽  
X Rays ◽  
Nitrogen Yield ◽  
Wide Range ◽  
Higher Doses ◽  
Limiting Values

Water vapor irradiated with X-rays in the presence of nitrous oxide gives mainly nitrogen and oxygen together with small amounts of hydrogen and, possibly, hydrogen peroxide. The yield of nitrogen, G(N2) = 3.0 ± 0.3, is constant over a wide range of conditions and G(O2) = 1.6 ± 0.3 after an induction period. The hydrogen yield is constant at low doses with G(H2) = 0.45 ± 0.1, but reaches a steady state at higher doses. The nitrogen yield is equated with the yield of scavengeable electrons in water vapor, the value g(e) = 3.0 ± 0.3 being in reasonable agreement with the theoretical value based on W(H2O) = 30 eV. Addition of other electron scavengers to water vapor containing nitrous oxide suppresses the nitrogen yield by competing efficiently for electrons. On the basis of their efficiency in suppressing the nitrogen yield, limiting values for the relative rates of reaction of N2O, SF6, CCl4, and HCl with electrons in water vapor are obtained and comparisons are made with their known electron attachment cross sections in the gas phase.

HYDROGEN FORMATION IN γ-IRRADIATED HYDROGEN CHLORIDE

1962 ◽  
Vol 40 (7) ◽  
pp. 1385-1393 ◽  
Author(s):  
D. A. Armstrong
Keyword(s):  
Hydrogen Chloride ◽  
Solid Hydrogen ◽  
Pure Liquid ◽  
Hydrogen Yield ◽  
Hydrogen Atoms ◽  
A Value ◽  
Low Concentrations ◽  
Electronically Excited ◽  
Γ Rays ◽  
Electronically Excited Molecules

Hydrogen yields from pure liquid and solid hydrogen chloride irradiated with Co60 γ-rays were [Formula: see text](liquid) = 6.50 ± 0.10 and [Formula: see text] (solid) = 3.30 ± 0.10 at −79 °C and −196 °C respectively. The yield from solid hydrogen chloride was only slightly reduced by the addition of chlorine; but the yield from liquid samples was reduced sharply by low concentrations of chlorine to a value of about 4.5, and then much more gradually by larger concentrations. A [Formula: see text] value of 2.1 persisted at 10 mole% chlorine. The results were interpreted in terms of the formation of hydrogen in the reactions[Formula: see text]and[Formula: see text]Reduction of the hydrogen yields by chlorine was attributed to the reactions[Formula: see text]and[Formula: see text]Values of k11/k15 and k11*/k15* were estimated to be 1.7 × 10−3 and 0.10 respectively, while those of GH and GH(hot) were 2.4 ± 0.2 and 4.0 ± 0.2. Electron scavenging by chlorine was considered as a less likely mechanism for reduction of the hydrogen yield. Sources of the thermal and hot hydrogen atoms were examined and it was suggested that the decomposition of electronically excited molecules might be an important mode of decomposition.

The Radiolysis of Water Vapor at Very High Dose Rates. II. Isotope Effects in the Hydrogen Yield from H2O–D2O Mixtures

1973 ◽  
Vol 51 (24) ◽  
pp. 4056-4061 ◽  
Author(s):  
A. W. Boyd ◽  
C. Willis ◽  
O. A. Miller
Keyword(s):  
Water Vapor ◽  
Isotope Effect ◽  
Isotope Effects ◽  
High Dose ◽  
Hydrogen Yield ◽  
Hydrogen Atoms ◽  
Dose Rates ◽  
Very High

The isotope effect in the formation of hydrogen has been measured for H2O–D2O mixtures (10–90% H2O, 0.5–1.0 mg ml−1, 412–138 °C) with and without 1 mol% SF6 at 2 × 1027 eV g−1 s−1. The values of α ((H/D) radiolytic hydrogen/(H/D) H2O–D2O) for the reactions of hydrogen atoms are in the range 3–6 varying with H/D ratio of the substrate. Consideration of possible mechanisms for these large α values leads to the conclusions that reaction of the hydrogen atoms to form hydrogen involves the substrate and that the species H3O may be formed as an intermediate.

THE RADIOLYSIS OF HCl–HBr MIXTURES

1963 ◽  
Vol 41 (5) ◽  
pp. 1104-1112 ◽  
Author(s):  
R. C. Rumfeldt ◽  
D. A. Armstrong
Keyword(s):  
Hydrogen Yield ◽  
Hydrogen Atoms ◽  
A Value ◽  
Excited Molecules

Bromine was the only halogen formed in irradiated mixtures of HCl and HBr. A study of its effect on the hydrogen yield from HCl showed that it reacted with the first hydrogen-forming species (or its precursor), and indicated the same yield for this species as did the earlier experiments with chlorine. The results were consistent with thermal hydrogen atoms, formed in the reaction[Formula: see text]as the first hydrogen-forming species, and hot hydrogen atoms, resulting from the dissociation of excited HCl molecules, as the second species.The hydrogen yield from liquid HBr at −79°C was a factor of two larger than that from liquid HCl at the same temperature, and in mixtures of the two the hydrogen yield increased gradually from a value characteristic of pure HCl [Formula: see text] to one characteristic of pure HBr [Formula: see text] The smaller yield from HCl cannot be explained by radical combinations:[Formula: see text] [Formula: see text]in the radiation tracks and must be attributed either to differences in the ion-combination reactions in the two liquids or to a genuinely greater yield of ions and/or dissociative excited molecules in HBr. The hydrogen yield from solid HBr at −196 °C was [Formula: see text].

THE RADIOLYSIS OF CYCLOHEXANE: IV. BINARY MIXTURES IN THE VAPOR PHASE

1961 ◽  
Vol 39 (9) ◽  
pp. 1769-1775 ◽  
Author(s):  
J. M. Ramaradhya ◽  
G. R. Freeman
Keyword(s):  
Experimental Data ◽  
Reaction Mechanisms ◽  
Excited Molecule ◽  
Hydrogen Yield ◽  
Hydrogen Atoms ◽  
Energy Excitation ◽  
Gaseous Mixtures ◽  
Straight Line ◽  
Positive Ion ◽  
Mechanisms Of Reactions

The variation of the hydrogen yield with the composition of binary gaseous mixtures containing cyclohexane and benzene, cyclohexene, or propylene is qualitatively similar to that in the liquid phase.The quantitative experimental data were tested against several possible reaction mechanisms and two mechanisms gave straight-line plots.One mechanism involved scavenging of hydrogen atoms. The values of the kinetic parameters derived from this mechanism might not be unreasonable in the mixtures of cyclohexane with cyclohexene or propylene. The values for benzene, however, seem less likely.The second mechanism involved the transfer of energy (excitation or ionization) from cyclohexane to the second substance. The values of the ratio of the rate constants, k7/k6, of the reactions[Formula: see text]is about 103 times greater in the gas than in the liquid phase. Consideration of possible detailed mechanisms of reactions [6] and [7] indicates that this difference is reasonable if C6H12** is a positive ion rather than an excited molecule.

Effect of Pressure on the Rates of Reaction of Hydrogen Atoms in the Radiolysis of Liquid Ethanol

1973 ◽  
Vol 51 (12) ◽  
pp. 2033-2040 ◽  
Author(s):  
Kamal N. Jha ◽  
Gordon R. Freeman
Keyword(s):  
Charge Transfer ◽  
Hydrogen Atom ◽  
Aromatic Ring ◽  
Rate Constants ◽  
Hydrogen Yield ◽  
Hydrogen Atoms ◽  
Solvated Electrons ◽  
Effect Of Pressure

Competition between the reactions[Formula: see text]and[Formula: see text]was measured at 296 K at 1 bar and 5.4 kbar. Values of k5/k3 at 1 bar and (ΔV5≠ − ΔV3≠) averaged between 1 bar and 5.4 kbar for several solutes S are: cyclohexene, 56, + 2.7 cm3/mol; hexene-1, 71, + 2.6 cm3/mol; phenol, 25, −3.8 cm3/mol; benzene, 12, −6.5 cm3/mol. The volume of activation of hydrogen atom addition to the aromatic ring is about 8 cm3/mol more negative than that of addition to a mono-olefin. Rate constants of reaction of solvated electrons with these solutes at 295 K, measured by the pulse-radiolysisspectroscopy technique, are (M−1 s−1): cyclohexene, <1 × 104; hexene-1, 1 × 105; benzene, 4 × 106; phenol, 5 × 107. The phenol reaction with e−solv does not reduce the hydrogen yield by a proportionate amount, so phenol "catalyses" the decomposition of e−solv to form hydrogen, perhaps via C6H5OH−solv → C6H5O−solv + H. The scavenging of hydrogen precursors by hexene-1, benzene, and aniline in n-hexane, reported in ref. 6, had [Formula: see text], −6, and −4 cm3/mol, respectively, all three of which may be attributed to hydrogen atom reactions. The yields of hydrogen from solutions of neohexane in cyclopentane at 1 bar and 5.4 kbar indicate that charge transfer occurs from cyclopentane to neohexane, and that the probability of charge transfer is independent of pressure. The methane yields from these solutions indicate that the decomposition of the neohexane ion formed by charge transfer from cyclopentane, to form methane, is inhibited by pressure.

Formation of surface layer of hydrogen in pure aluminum

2019 ◽  
Vol 484 (1) ◽  
pp. 56-60
Author(s):  
D. A. Indejtsev ◽  
E. V. Osipova
Keyword(s):  
Surface Layer ◽  
Hydrogen Atom ◽  
Ab Initio ◽  
Pure Aluminum ◽  
Hydrogen Atoms ◽  
Energy Characteristics ◽  
Aluminum Crystal

Hydrogen atom behavior in pure aluminum is described by ab initio modelling. All main energy characteristics of the system consisting of hydrogen atoms in a periodic aluminum crystal are found.

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