Journal Archive Collections
Permanent URI for this communityhttp://localhost:4000/handle/123456789/16937
Browse
10 results
Search Results
Item Reaction of Hydrogen Atoms with Ethane(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (08), 1974) Camilleri, Patrick; Marshall, Roger M.; Purnell, J. HowardThe reaction between hydrogen atoms and ethane has been studied in a flow-discharge system over the wide temperature range 503–753 K at pressures between 8 and 16 Torr. The major products are methane and ethane, reformed by methyl recombination. Minor products are propane and ethylene with traces of n-butane. The detailed mechanism has been established and computer calculations have been used to derive the set of best-fit rate parameters which reproduce all the experimental results. The results of this work yield the result k1/cm3 mol–1 s–1= 1014.27 ± 0.13 exp (–40.9 ± 1.6 kJ mol–1/RT); H + C2H6→ H2+ C2H5. (1) A survey of all published data some of which have been revised by us to take account of wrongly assumed stoichiometry in the original work, shows that, over a range of 1000 K, the data can be represented by the Arrhenius expression, k1/cm3 mol–1 s–1= 1014.12 ± 0.09 exp (–39.2 ± 0.9 kJ mol–1RT). There is thus no reason to suppose curvature in this plot as has been suggested. Values of the rate constants for the reactions H + C2H5→ 2CH3(2), CH3+ H → CH4(5), and, H + C2H5→ H2+ C2H4(11), are found to be k2/cm3 mol–1 s–1= 1013.57, k5/cm3 mol–1 s–1= 1012.04 at 8 Torr, 1012.20 at 12 Torr and 1012.34 at 16 Torr and k11/cm3 mol–1 s–1= 1012.23. We have reassessed our earlier data on the reaction of hydrogen atoms with ethylene in the light of the recent “low” values for the rate constant of ethyl recombination. From this, we find values for k2 and k5 at 290 K which are, respectively, lower and higher than the corresponding values in the range 503–753 K. It is shown that the slight temperature dependence observed is consistent with the order of reactions (2) and (5).Item Reactions of Energetic Hydrogen Atoms with Simple Hydrocarbons: Part 3.—Bromine Scavenger Effects(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (1-6), 1974) Hall, Richard B.; Malcolme-Lawes, David J.The effect of small amounts of bromine on the hot abstraction and substitution yields from recoil tritium atoms reacting with methane are examined in the presence of neon, argon and xenon. It is concluded that bromine reduces the yield of both products by competing with the hydrocarbon for the hot atoms, and that the moderator influences the magnitude of the excitation function for HT production (through collisional dissociation of excited HT) so that the scavenger effect becomes more pronounced in the order Ne < Ar < Xe moderator.Item Electron paramagnetic resonance study of hydrogen atoms trapped in γ-irradiated Y type zeolites exchanged with different cations(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (1-6), 1974) Abou-Kais, Antoine; Vedrine, Jacques C.; Massardier, Jean; Dalmai-Imelik, GiseleH atoms trapped after the γ-irradiation at 77 K of Y type zeolites exchanged with different cations have been studied using e.p.r. spectroscopy. The H atom yield is dependent on the acidic structural OH group content and it is postulated that the mechanism of formation and trapping of H atoms follows the following equilibrium: [graphic omitted] The H atom yield is related to the acidity and mobility of the hydrogen of the hydrogen of the hydroxyl groups and to the trapping strength. The trapping strength of H atoms, characterized by the values of both the hyperfine coupling constant with respect to the free H atom, and the activation energy of recombination, is strongly dependent on the nature of the exchanged cation, and follows the sequence K > Na [double greater-than, compressed] Ca > La.Item Reaction between Hydrogen Atoms and Nitrogen Dioxide(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (1-6), 1974) McKenzie, Alan; Mulcahy, Maurice F. R.; Steven, James R.The stoichiometry and mechanism of the overall reaction between H atoms and NO2 has been studied by e.s.r. spectrometry combined with computer simulation. The stoichiometry 2H + 3NO2→3NO + O2+ H2O customarily assumed in titrating H by NO2 cannot be relied upon when the titration is conducted in an acid-washed quartz flow-tube. The concentration of NO2 required precisely to consume an H concentration, [H]0, of about 10–9 mol cm–3 or less can vary from about 1.1 [H]0 to 1.5 [H]0 depending on the activity of the surface. The concentrations of OH observed during reaction are also variable. On the H-rich side, the results can be explained by including in the reaction mechanism the surface reaction suggested by previous mass spectrometric work, namely H + OH→H2O. (5) The kinetics of reaction (5) are complex and, when H is in moderate excess ([H]0/[NO2]0≈1.2), the reaction is effectively zero order in [H]. When excess [NO2] over [H] is present originally, the concentration of OH in the system is not determined solely by known gas-phase reactions including OH + NO2+ M and OH + NO + M. Again it appears that one or more surface reactions of OH occur.Item Reactions of Energetic Hydrogen Atoms with Simple Hydrocarbons Part 1.—The Effect of Moderators(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1973, 69 (5), 1973) Terry, R.; Baker, K.The reactions of recoil tritium atoms with ethane have been studied in the presence of N2 and CF^ moderators. The results suggest that collisional dissociation of excited HT, initially produced by direct reaction, may be more important in determining the ratio of final products than the commonly described effect of energy shadowing. It is suggested that hydrocarbons behave essentially as carbon atoms as far as their ability to collisionally dissociate HT is concerned, and that moderators which consist of groups which are similar in mass to carbon atoms, exert very little effect on observed product ratios.Item Kinetics of the Reaction of Hydrogen Atoms with 1,I-Difluoroethylene(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1973, 69 (1), 1973) Teng, L.; Jones, W. E.Hydrogen atoms generated in a Wood-Bonhoeflcr discharge were reacted with 1,1-difluoroethylene. The products of the reaction were: HF, C2H4, C2H6, C2H2, CH4, C3H6, n-C4H10, ( 3H8 and C2H3F. With the exception of HF, n-C4H10 and C3H8, al! were quantitatively studied over the temperature range 303-603 K. The kinetics and mechanism of the H atom4-CF2CH2 reaction have been studied in detail. The rate constants have been calculated for each step of the mechanism for three temperatures allowing determination of activation energies. The calculation of the rate constants and testing of the mechanism were accomplished by numerical integration of the simultaneous differential equations for each species involved in the reaction.Item Electron Spin Resonance Study of the Reaction of Hydrogen Atoms with Hydrogen Sulphide(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1973, 69 (2), 1973) Bradley, John N.; Trueman, Susan P.; Whytock, David A.; Zaleski, Thomas A.The reaction between H atoms and hydrogen sulphide, with and without added nitric oxide, has been studied by following the H atom, S atom and SH radical concentrations with time using electron spin resonance detection. The results are fully explained by the mechanism (1)–(4) H + H2S→H2+ SH, k1= 5.0 × 108 l. mol–1 s–1(1), H + SH → H2+ S, k2= 2.5 × 1010 l. mol–1 s–1(2), SH + NO → stable species, k3= 6.3 × 108 l. mol–1 s–1(3), SH + SH → H2S + S, k4= 7.8 × 109 l. mol–1 s–1. (4) with no evidence for significant surface effects (the walls were coated with boric acid). The results demonstrate conclusively that reaction (2) is very important in this system and that previous measurements of k1 which neglect this reaction may require correction.Item Reaction of Hydrogen Atoms with Nitrous Oxide(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1973, 69 (2), 1973) Baldwin, R. R.; Gethin, A.; Walker, R. W.The velocity constant of the reaction H + N2O → N2+ OH (22) has been obtained at 500°C by the addition of N2O to slowly reacting mixtures of H2+ O2+ He and measurement of the relative rates of formation of N2 and H2O. The ratio k22/k2= 0.64 ± 0.07 gives k22= 2.6 × 106 l. mol–1 s–1, the error of ± 30–40% being largely due to the uncertainty in k2. H + O2→ OH + O. (2) Combination with other measurements gives the Arrhenius parameters A22= 7.6 × 1010 l. mol–1 s–1, E22= 15.1 ± 1.0 kcal mol–1.Item Threshold Energy in the Abstraction Reaction between Hydrogen Atoms and Cyclohexane(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (9), 1972) Fink, Richard D.; Nicholas, John E.The reactions of deuterium atoms of selected translational energies with cyclohexane have been investigated. The atoms were generated by the photochemical dissociation of hydrogen halides with a series of effectively monochromatic light sources. The relative probability of atoms undergoing reaction or energy loss on collision with cyclohexane was determined at each initial energy and the phenomenological threshold energy for the abstraction reaction was measured at 36 ± 3 kJ mol–1.Item Kinetics of the Reactions of Hydrogen Atoms with Ethylene and Vinyl Fluoride(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (7), 1972) Teng, L; Jones, W. E.Hydrogen atoms generated in a Wood-Bonhoeffer discharge were reacted with vinyl fluoride and ethylene. The products of the vinyl fluoride reaction were: HF, C2H4, C2H6, C2H2, CH4, C3H6, n-C4H10 and C3H8. With the exception of HF, all were quantitatively studied over the temperature range 303-603 K. The reaction of ethylene under similar conditions gave: C2H6, C3H8, n-C4Hi0 and CH4. The kinetics and mechanisms of both reactions have been studied in detail. The rate constants have been calculated for each step of the mechanisms for three temperatures allowing determination of activation energies. The calculation of the rate constants and testing of the mechanisms was accomplished by numerical integration of the simultaneous differential equations for each species involved in the reactions.