THE REACTION OF DEUTERIUM ATOMS WITH ETHYLENE

1956 ◽  
Vol 34 (8) ◽  
pp. 1061-1073 ◽  
Author(s):  
S. Toby ◽  
H. I. Schiff
Keyword(s):  
Isotopic Composition ◽  
Isothermal Calorimetry ◽  
Reaction Rates ◽  
Recombination Coefficient ◽  
Tungsten Filament ◽  
Hydrogen Atoms ◽  
Atom Concentration ◽  
Metaphosphoric Acid ◽  
Detector Position ◽  
Reactant Flow

Deuterium was dissociated on a hot tungsten filament and the atom concentration measured by isothermal calorimetry. The recombination coefficient of deuterium atoms on a glass surface, coated with metaphosphoric acid, was found to be 3.8 × 10−5, and similar to that found for hydrogen atoms. The reactions of H-atoms and D-atoms with ethylene were found to be very rapid. The effects on the yields of the products and on their isotopic composition of variations of reactant flow rate, atom concentration, pressure, and atom-detector position were studied. The major products were methanes, ethanes, and ethylenes, with minor amounts of propanes and butanes. The methanes were always highly deuterated while the ethanes were slightly deuterated. A mechanism is proposed to explain the observations based on a flow pattern in the reaction zone. The possibility of differences in the reaction rates of variously deuterated intermediates is also discussed.

scholarly journals The photolysis of ammonia

1940 ◽  
Vol 175 (961) ◽  
pp. 187-207 ◽  
Keyword(s):  
Hydrogen Atom ◽  
Preceding Paper ◽  
Ammonia Molecule ◽  
Experimental Techniques ◽  
Hydrogen Atoms ◽  
Atom Concentration ◽  
Important Discrepancy

It has been shown in the preceding paper that the hypothesis that hydrazine is responsible for the anomalously low hydrogen atom concentration in the decomposition of ammonia must be abandoned. In order to explain this important discrepancy some new experimental techniques require to be developed which will settle the matter without appeal to further hypotheses. There are two general explanations of the discrepancy: (1) the hydrogen atoms are not produced as fast as that calculated on the assumption that every ammonia molecule absorbing a quantum necessarily decomposes, (2) that some entity not yet recognized removes hydrogen atoms at a rate faster than that at which they normally recombine. In this paper methods will be described in which these two problems are solved, and finally there is a discussion of the photochemistry of ammonia in the light of the new results obtained during these experiments.

Exchange reactions of olefins with deuterium oxide on ion-exchanged X-type zeolites

1971 ◽  
Vol 321 (1545) ◽  
pp. 259-273 ◽  
Keyword(s):  
Active Sites ◽  
Deuterium Oxide ◽  
Reaction Rates ◽  
Main Reaction ◽  
Exchange Reactions ◽  
Hydrogen Atoms ◽  
Carbonium Ion ◽  
Mass Spectrometric Technique ◽  
Carbonium Ions ◽  
Cation Charge

Reactions of propylene, ethylene, but-1-ene , isobutene and isobutane with D 2 O on ion-exchanged X-type zeolites have been followed by a mass spectrometric technique. Exchange was usually the main reaction but polymerization of olefins also occurred with some catalysts. All the hydrogen atoms in isobutene were exchanged at similar rates by a stepwise process but with propylene only five atoms were replaced. Exchange was complicated by simultaneous isomerization with but-1-ene. Isobutane reacted only at high temperatures but gave multiply exchanged products. The order of activity for exchange was isobutene ⪢ but-1-ene > propylene ⪢ ethylene, isobutane, and this order appeared to reflect the relative ease of formation of carbonium ions from the hydrocarbons. The character of the exchange reactions as well as the rates were in accord with mechanisms involving carbonium ion intermediates . The order of activity of the zeolites for the exchange of propylene was CeX, LaX > NiX, CuX, CoX > CaX > NaX and a correlation was found to exist between the apparent activation energy for exchange and a function of the cation charge. Reaction rates on NiX and CeX increased with increasing degree of ion-exchange and decreased with increasing amounts of D 2 O. There was evidence that in some cases the active sites were associated with acidic OH(OD) groups rather than the cations themselves.

scholarly journals THE STUDY OF ELECTRICALLY DISCHARGED O2 BY MEANS OF AN ISOTHERMAL CALORIMETRIC DETECTOR

1959 ◽  
Vol 37 (10) ◽  
pp. 1680-1689 ◽  
Author(s):  
L. Elias ◽  
E. A. Ogryzlo ◽  
H. I. Schiff
Keyword(s):  
Gas Phase ◽  
Molecular Oxygen ◽  
Surface Recombination ◽  
Negative Temperature ◽  
Recombination Coefficient ◽  
Third Order ◽  
Atom Concentration ◽  
Electrodeless Discharge ◽  
First Order ◽  
A Value

Molecular oxygen was subjected to an electrodeless discharge in the pressure range 0.1–3 mm Hg. The oxygen atom concentration was measured as a function of time in a flow system by means of a movable atom detector which consisted of a platinum wire coated with a suitable catalyst for atom recombination. The atom concentration was calculated from the heat liberated when the detector was operated under isothermal conditions. The surface recombination was found to be first order in the atom concentration. A value of 7.7 × 10−5 was obtained for the recombination coefficient (γ) on Pyrex. No temperature dependence for γ was observed. The gas phase recombination of oxygen atoms was found to be consistent with the mechanism[Formula: see text]The rate constant for the third-order reaction was found to have a value of 1.0 × 1014 cc2 mole−2 sec−1, and a small negative temperature dependence.Evidence was also obtained for the presence of considerable amounts of excited molecular oxygen in electrically activated O2.

Inorganic Proton Exchange Membranes

2006 ◽  
Author(s):  
Timothy Reissman ◽  
Austin Fang ◽  
Ephrahim Garcia ◽  
Brian J. Kirby ◽  
Romain Viard ◽  
...  
Keyword(s):  
Porous Silicon ◽  
Direct Methanol Fuel Cells ◽  
Reaction Rates ◽  
Cathode Side ◽  
Infrared Spectrometry ◽  
Silicon Membrane ◽  
Binding Agent ◽  
Hydrogen Atoms ◽  
Mechanical Filter ◽  
Direct Methanol

Direct Methanol Fuel Cells (DMFCs) offer advantages from quick refills to the elimination of recharge times. They show the most potential in efficient chemical to electrical energy conversion, but currently one major source of inefficiency within the DMFC system is the electrolyte allowing fuel to cross over from the anode to cathode. Proprietary DuPont™ Nafion® 117 has been the standard polymer electrolyte thus far for all meso-scale direct methanol power conversion systems, and its shortcomings consist primarily of slow anodic reaction rates and fuel crossover resulting in lower voltage generation or mixed potential. Porous Silicon (P-Si) is traditionally used in photovoltaic and photoluminescence applications but rarely used as a mechanical filter or membrane. This research deals with investigations into using P-Si as a functioning electrolyte to transfer ions from the anode to cathode of a DMFC and the consequences of stacking multiple layers of anodes. Porous silicon was fabricated in a standard Teflon cylindrical cell by an anodization process which varied the current density to etch and electro-polish the silicon membrane. The result was a porous silicon membrane with approximately 1.5 μm pore sizes when optically characterized by a scanning electron microscope. The porous membranes were then coated in approximately 0.2 mg/cm2 Pt-Ru catalyst with a 10% Nafion® solution binding agent onto the anode. Voltage versus current data shows an open circuit voltage (OCV) of 0.25V was achieved with one layer when operating at 20°C. When adding a second porous silicon layer, the OCV was raised to approximately 0.32V under the same conditions. The experimental data suggested that the current collected also increased with an additional identical layer of anode prepared the same way. The single difference was that the air cathode side was surface treated with 0.1 mg of Pt black catalyst combined with a 10% Nafion® binding agent to aid in the recombination of hydrogen atoms to form the water byproduct. Porous silicon endurance runs with 2ml of 3% by volume methanol (0.7425M) fuel dissolved in water showed an operating voltage was generated for approximately 3 hours before the level dropped to approximately 65% of the 0.25V maximum voltage. Endurance runs with a second layer added extended the useful cell life to approximately 5 hours under the same conditions. In an effort to quantify these layering results, Fourier Transform Infrared Spectrometry was conducted on a number of samples to verify decreased methanol concentration present in the second layer.

Electron spin resonance study of the reaction of hydrogen atoms with methane

1994 ◽  
Vol 72 (3) ◽  
pp. 600-605 ◽  
Author(s):  
Paul-Marie Marquaire ◽  
Ashok Ghose Dastidar ◽  
Kim C. Manthorne ◽  
Philip D. Pacey
Keyword(s):  
Electron Spin Resonance ◽  
Electron Spin ◽  
Activation Barrier ◽  
Heat Of Formation ◽  
State Theory ◽  
Electron Spin Resonance Study ◽  
Methyl Radical ◽  
Hydrogen Atoms ◽  
Atom Concentration ◽  
Spin Resonance

The reaction: H + CH4 → CH3 + H2 has been investigated in a flow system between 348 and 421 K. Hydrogen atoms were generated in a microwave discharge, introduced to the reactor through a movable injector, and monitored by electron spin resonance. After an initial decay attributed to reaction with impurity, the hydrogen atom concentration decayed in a pseudo-first-order manner. Ethane was detected by gas chromatography, consistent with its formation by the following reaction: 2CH3 → C2H6. The amount of ethane formed at 421 K was only 0.015 times the amount of hydrogen atoms reacting. Most methyl radicals were assumed to have been removed by the process: H + CH3 + M → CH4 + M. Because of this process, two hydrogen atoms were removed each time the title reaction occurred. Applying this stoichiometric factor, the rate constant for the elementary reaction was calculated to be 2.5 × 103 L mol−1 s−1 at 348 K, increasing to 2.0 × 104 L mol−1 s−1 at 421 K. Most of the previous discrepancy between kinetics and thermochemistry has been eliminated; the exothermicity at 0 K was reduced to 0.8 ± 0.4 kJ mol−1, which corresponds to a standard heat of formation of the methyl radical of 145 kJ mol−1. Properties of the activation barrier have been inferred from the experimental data with the aid of transition state theory. The fitted barrier height was 63 ± 1 kJ mol−1, the average of five low-frequency vibrational term values was 640 ± 30 cm−1, and the characteristic tunnelling temperature was 500 ± 30 K.

scholarly journals The basic reactions in the upper atmosphere II. The theory of recombination in the ionized layers

1947 ◽  
Vol 192 (1028) ◽  
pp. 1-16 ◽  
Keyword(s):  
Ionization Potential ◽  
Recent Work ◽  
Reaction Rates ◽  
Upper Atmosphere ◽  
Recombination Process ◽  
Recombination Coefficient ◽  
Lower Ionization Potential ◽  
Two Alternatives

Recombination in the ionized layers is discussed. It is pointed out that the results of recent work make the ionic recombination theory very difficult to maintain. Consideration is therefore given to two alternatives, the dust recombination theory and the molecular recombination theory. It is concluded that of these only the latter is at all promising. In the E layer the recombination process would be O + 2 + e → O׳ + O״, while in F 1 the effective reactions would be O + + XY → XY + + O XY + + e → X' + Y' }, N + 2 + e → N' + N'', and N + 2 + XY → XY + + N 2 XY + + e → X' + Y' }. The molecule XY possesses a lower ionization potential than O and need form only a very small fraction of the upper atmospheric content at the altitudes concerned. It is not identified but may be O 2 or NO. The reaction involving O + must be introduced, as otherwise the concentration of this ion would build up to impossibly large values. In F 2 the same reactions would be supposed to occur as in F 1 , but the reduced amount of XY would lead to a lower and pressure-dependent recombination coefficient. Confirmation of the theory must await proper determination of the reaction rates.

The dissociation of hydrogen by tungsten

1936 ◽  
Vol 32 (4) ◽  
pp. 648-652 ◽  
Author(s):  
G. Bryce
Keyword(s):  
Tungsten Oxide ◽  
Constant Temperature ◽  
Atomic Hydrogen ◽  
Square Root ◽  
Tungsten Filament ◽  
Hydrogen Atoms ◽  
Production Of Hydrogen

The dissociation of hydrogen by a hot tungsten filament has been studied under conditions such that all the atomic hydrogen produced is effectively removed by reaction with molybdenum or tungsten oxide. The rate of production of atomic hydrogen is many times greater than was inferred from earlier work. With the tungsten at constant temperature the rate of dissociation is proportional to the square root of the pressure. A formula is given for the rate of production of hydrogen atoms per sq. cm. of the tungsten per second.

Comparison of muonium and positronium with hydrogen atoms in their reactions towards solutes containing amide and peptide linkages in water and micelle solutions

1989 ◽  
Vol 67 (1) ◽  
pp. 120-126 ◽  
Author(s):  
Mary V. Barnabas ◽  
Krishnan Venkateswaran ◽  
David C. Walker
Keyword(s):  
Carbonyl Group ◽  
Rate Constants ◽  
Reaction Rates ◽  
Hydrogen Atoms ◽  
Methyl Group ◽  
Hydrated Electrons

Rate constants have been sought for the reaction of muonium (Mu) and o-positronium (Ps) with solutions of thirteen solutes containing [Formula: see text] the groups. Values of k range from <105 M−1 s−1 to 3 × 1010 M−1 s−1 and show a variety of trends. For instance, Mu adds across the carbonyl group much faster than does H, but abstracts from an adjacent methyl group more slowly. Mu adds exceptionally efficiently to the thiocarbonyl group. Abstraction reactions are identified by large enhancements in reaction rates when localized in micelles. Ps behaves quite differently to the others in neither abstracting nor adding to these compounds, consistent with it not being a pseudo-isotope of hydrogen. Keywords: muonium, positronium, hydrogen, hydrated electrons, micelles.

The chemical structure of premixed fuel-rich methane flames: the effect of hydrocarbon species in the secondary reaction zone

1991 ◽  
Vol 433 (1887) ◽  
pp. 1-21 ◽  
Keyword(s):  
Reaction Zone ◽  
Chemical Structure ◽  
Reaction Rates ◽  
Secondary Reaction ◽  
Partial Equilibrium ◽  
Oh Radicals ◽  
Primary Reaction ◽  
Bimolecular Reactions ◽  
Atom Concentration ◽  
Secondary Reaction Zone

In a previous paper the analysis of a fuel-rich, ф =1.60, methane flame using a four-stage molecular beam inlet to a quadrupole mass spectrometer was described. The results were used to investigate the chemical structure of the primary reaction zone of the flame. In this paper, results from a richer flame, ф = 2.00, are presented and analysed. This premixed, laminar, flat flame had the following composition (all molar percentages) and conditions: 35.0% (CH 4 ), 35.0% (O 2 ), 30% (Ar); pressure = 8.00 kPa; cold-gas velocity at 293 K = 0.47 m s -1 . Mole fraction profiles through each flame were measured for a large number of stable and radical species, and those for the ф = 2.00 flame are presented in this paper and are compared with the results from the ф = 1.60 flame published earlier. Analysis and discussion in the present paper concentrates on the secondary reaction zone of both fuel-rich flames. Comparison of the profiles shows that hydrocarbon species survive the primary reaction zone in increasing concentrations as ф increases. It is shown that the reaction H + O 2 ⇌ OH + O (21, -21 ) does not achieve the partial equilibrium condition that is found in leaner flames, although the remaining bimolecular reactions of the H 2 -O 2 system do so. The competition between various species for the H, O and OH radicals is analysed using a convenient parameter which allows comparison of reaction rates and which has been called the 'characteristic reaction time’, r . It is concluded that the direct cause of the inability of (21, -21) to achieve partial equilibrium is the removal of O atoms from the available pool of H, O and OH radicals by reaction with hydrocarbon species, particularly C 2 H 2 . The rate of decrease of the H atom concentration in the secondary reaction zone is shown to be too fast to be the result of termolecular recombination reactions; it is suggested that the cause is the rapid response of the fast bimolecular reactions of the H 2 -O 2 system to the removal of O atoms via OH + H → O + H 2 , (-22) OH + OH → O + H 2 O (-23) thus reducing the concentrations of H and OH radicals. This mechanism explains the reduction in the excesses of the H, O and OH radicals above their thermodynamic equilibrium levels that is observed with increasing ф . It is concluded that it is possible to view a rich flame as consisting entirely of an extended primary reaction zone in which the concentrations of the H, O and OH radicals are controlled by bimolecular reactions throughout.

Sign in / Sign up

Export Citation Format

Share Document