Mesure de la constante de vitesse de réaction des atomes d'hydrogène sur l'éthane et le propane en réacteurs tubulaire et parfaitement agité ouverts

1978 ◽  
Vol 56 (3) ◽  
pp. 392-401 ◽  
Author(s):  
Jacques Lede ◽  
Jacques Villermaux
Keyword(s):  
Hydrogen Atom ◽  
Rate Constant ◽  
Electrical Discharge ◽  
Room Temperature ◽  
Hydrogen Atoms ◽  
Atom Concentration ◽  
Sensitive Method ◽  
Good Agreement

The rate constant for the reaction of hydrogen atoms, generated by electrical discharge, with ethane and propane has been studied in tubular and perfectly stirred open reactors. Measurements are made with a new and very sensitive method of analysis of the hydrogen atom concentration. The results obtained near room temperature are in good agreement with those of other authors operating at much higher temperatures. The following estimates may be made:[Formula: see text]

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.

The reaction of hydrogen atoms with ethylene

1970 ◽  
Vol 316 (1527) ◽  
pp. 575-591 ◽  
Keyword(s):  
Hydrogen Atom ◽  
Rate Constant ◽  
Recombination Reaction ◽  
Methyl Radicals ◽  
Methyl Radical ◽  
Hydrogen Atoms ◽  
Ethyl Radical ◽  
Cracking Reaction ◽  
Computer Calculations ◽  
First Time

A detailed study has been made of the products from the reaction between hydrogen atoms and ethylene in a discharge-flow system at 290 ± 3 K. Total pressures in the range 8 to 16 Torr (1100 to 2200 Nm -2 ) of argon were used and the hydrogen atom and ethylene flow rates were in the ranges 5 to 10 and 0 to 20 μ mol s -1 , respectively. In agreement with previous work, the main products are methane and ethane ( ~ 95%) together with small amounts of propane and n -butane, measurements of which are reported for the first time. A detailed mechanism leading to formation of all the products is proposed. It is shown that the predominant source of ethane is the recombination of two methyl radicals, the rate of recombination of a hydrogen atom with an ethyl radical being negligible in comparison with the alternative, cracking reaction which produces two methyl radicals. A set of rate constants for the elementary steps in this mechanism has been derived with the aid of computer calculations, which gives an excellent fit with the experimental results. In this set, the values of the rate constant for the addition of a hydrogen atom to ethylene are at the low end of the range of previously measured values but are shown to lead to a more reasonable value for the rate constant of the cracking reaction of a hydrogen atom with an ethyl radical. It is shown that the recombination reaction of a hydrogen atom with a methyl radical, the source of methane, is close to its third-order region.

DYNAMICS OF THE N(2D)+H2 REACTION ON THE $\tilde{X}^2 A^{\prime\prime}$ SURFACE, PROPAGATING REAL WAVE PACKETS WITH AN ARCCOS MAPPING OF THE HAMILTONIAN

2003 ◽  
Vol 02 (04) ◽  
pp. 547-551 ◽  
Author(s):  
PAOLO DEFAZIO ◽  
CARLO PETRONGOLO
Keyword(s):  
Rate Constant ◽  
Cross Sections ◽  
Room Temperature ◽  
Wave Packets ◽  
Flux Analysis ◽  
Title Reaction ◽  
Angular Momentum Quantum Number ◽  
Insertion Mechanism ◽  
Temperature Rate ◽  
Good Agreement

We have investigated the dynamics of the title reaction with the Gray and Balint-Kurti approach, which propagates real wave packets (WP) under an arccos mapping of a scaled and shifted Hamiltonian. We have considered H 2 rotational quanta j=0 and 1 and obtained reaction probabilities using reactant coordinates and the flux analysis. We have calculated accurate reaction probabilities for total angular momentum quantum number J=0, centrifugal-sudden probabilities for J>0, cross sections, and the room temperature rate constant. The present cross sections are in good agreement with previous quasiclassical trajectory (QCT) results and the theoretical rate constant compares rather well with that observed. WP snapshots show that the reaction occurs via a C2v insertion mechanism, confirming previous QCT calculations.

BrHgO• + C2H4 and BrHgO• + HCHO in Atmospheric Oxidation of Mercury: Determining Rate Constants of Reactions with Pre-Reactive Complexes and a Bifurcation

2019 ◽  
Author(s):  
Khoa T. Lam ◽  
Curtis J. Wilhelmsen ◽  
Theodore Dibble
Keyword(s):  
Hydrogen Atom ◽  
Quantum Chemistry ◽  
Transition State ◽  
Rate Constant ◽  
Rate Constants ◽  
Minimum Energy ◽  
Atmospheric Oxidation ◽  
Minimum Energy Path ◽  
Oh Radical ◽  
Hydrogen Atoms

Models suggest BrHgONO to be the major Hg(II) species formed in the global oxidation of Hg(0), and BrHgONO undergoes rapid photolysis to produce the thermally stable radical BrHgO•. We previously used quantum chemistry to demonstrate that BrHgO• can, like OH radical, readily can abstract hydrogen atoms from sp<sup>3</sup>-hybridized carbon atoms as well as add to NO and NO<sub>2</sub>. In the present work, we reveal that BrHgO• can also add to C<sub>2</sub>H<sub>4</sub> to form BrHgOCH<sub>2</sub>CH<sub>2</sub>•, although this addition appears to proceed with a lower rate constant than the analogous addition of •OH to C<sub>2</sub>H<sub>4</sub>. Additionally, BrHgO• can readily react with HCHO in two different ways: either by addition to the carbon or by abstraction of a hydrogen atom. The minimum energy path for the BrHgO• + HCHO reaction bifurcates, forming two pre-reactive complexes, each of which passes over a separate transition state to form a different product.

The mechanism of the pyrolysis of 2, 2, 3, 3-tetramethylbutane

1978 ◽  
Vol 363 (1715) ◽  
pp. 503-523 ◽  
Keyword(s):  
Hydrogen Atom ◽  
Rate Constant ◽  
Rate Constants ◽  
Volume Ratio ◽  
Reaction Scheme ◽  
Secondary Source ◽  
Kinetic Characteristics ◽  
Hydrogen Atoms ◽  
Reaction Conditions ◽  
Total Product

The pyrolysis of 2, 2, 3, 3-tetramethylbutane (TMB) was investigated in the ranges 699-735 K and 3-19 Torr (0.4-2.5 kPa) at up to 4% decomposition. The reaction is strongly self-inhibited and sensitive to the surface/volume ratio of the reaction vessel. A simple Rice-Herzfeld chain terminated by the heterogeneous removal of hydrogen atoms is proposed for the initial, uninhibited reaction generating isobutene and hydrogen in a 2:1 ratio. Self-inhibition is due to abstraction by hydrogen atoms of hydrogen atoms from product isobutene giving resonance-stabilized 2-methylallyl radicals which participate in homogeneous termination reactions. The kinetic characteristics of the major primary products (> 95% on a mole basis), isobutene and hydrogen, are accounted for when reasonable values are assumed for the rate constants for hydrogen atom abstraction by hydrogen atoms from TMB and from isobutene and for initiation and heterogeneous termination of the chain reaction. The kinetic characteristics of the formation of methane and propene (2-4% of total product) are accounted for by the secondary reaction scheme H + i-C 4 H 8 → i-C 4 H 9 , i-C 4 H 9 → CH 3 + C 3 H 6 , CH 3 + TMB → CH 4 + C 8 H 17 , when a reasonable value for the rate constant for the hydrogen atom addition to isobutene is assumed. The kinetic characteristics of the formation of ethene ( ca . 0.1% of total product) are accounted for by the tertiary reaction scheme H + C 3 H 6 → n -C 3 H 7 n -C 3 H 7 → CH 3 + C 2 H 4 , when a reasonable value for the rate constant for the hydrogen atom addition to propene is assumed. The kinetic characteristics of the formation of isobutane ( ca . 1% of total product) are much less affected by an increase in surface/volume ratio of the reactor than are those of the other products. A heterogeneous, secondary source is suggested, viz. 1/2H 2 ( g ) ⇌ H (wall), H (wall) + t-C 4 H 9 ( g ) ⇌ i-C 4 H 10 ( g ), which can generate the observed dependence of the isobutane yield on the reaction conditions but the reasonableness or otherwise of the values of the equilibrium and rate constants it is necessary to postulate is impossible to assess without further work designed specifically to investigate this problem.

Monte-Carlo simulation of hydrogen-atom recombination

1973 ◽  
Vol 333 (1595) ◽  
pp. 419-434 ◽  
Keyword(s):  
Hydrogen Atom ◽  
Cross Section ◽  
Rate Constant ◽  
Relative Velocity ◽  
Classical Trajectory ◽  
Hydrogen Atoms ◽  
Order Of Magnitude ◽  
The Cross ◽  
The Right ◽  
Right Order

Classical trajectory calculations have been used to calculate the cross-section (and hence the rate constant) for the recombination of hydrogen atoms on a third hydrogen atom, in the temperature range 500–6000 K. The model involves the stabilization of a quasi-bound molecule in an encounter with the third atom. The results indicate that the cross-section for direct stabilization is small and insensitive to the relative velocity, whereas the cross-section for exchange stabilization is large at low velocities and decreases rapidly as the relative velocity is increased. The calculated rate constant, although of the right order of magnitude at 500 K, does not exhibit the anomalous features previously observed experimentally at higher temperatures.

Rate and Rate-Determining Step of Hydrogen-Atom-Induced Strand Breakage in Poly(U) in Aqueous Solution under Anoxic Conditions

1985 ◽  
Vol 40 (3-4) ◽  
pp. 247-253 ◽  
Author(s):  
E. Bothe ◽  
H. Selbach
Keyword(s):  
Aqueous Solution ◽  
Hydrogen Atom ◽  
Rate Constant ◽  
Strand Break ◽  
Hydrogen Atoms ◽  
Anoxic Conditions ◽  
Rate Determining Step ◽  
Strand Breakage ◽  
Break Formation ◽  
Ribose Moiety

The rate constant for strand breakage in poly(U) after reaction with hydrogen atoms in deoxygenated aqueous solution has been determined to be k = 1.5 s-1 at pH = 4-5 and 24 °C. Dithiothreitol has been found to prevent strand break formation by reacting with H-adduct radicals of poly(U) with a rate constant of 5 × 106 M-1 s-1. It is concluded that the rate-deter­mining step in H atom-induced strand breakage in poly(U) at pH ≦ 6 is the decay of uracil moiety H-adduct radicals via H-abstraction from the ribose moiety.

scholarly journals Experimentelle und semi-empirische Protonen-Hyperfein- kopplungen von 1.3-Benzodioxol-Radikal-Kationen und ihre Korrelation mit Reaktivitäten in elektrophilen Substitutionen

1982 ◽  
Vol 37 (7) ◽  
pp. 680-687 ◽  
Author(s):  
Jörg Fleischhauer ◽  
Sun Ma ◽  
Wolfgang Schleker ◽  
Klaus Gersonde ◽  
Hans Twilfer
Keyword(s):  
Experimental Data ◽  
Perturbation Theory ◽  
Hyperfine Splitting ◽  
Electrophilic Substitution ◽  
Room Temperature ◽  
Hydrogen Atoms ◽  
Substitution Reactions ◽  
X Band ◽  
Band Spectra ◽  
Good Agreement

Abstract The solution ESR X-band spectra of 1.3-benzodioxole (methylenedioxybenzene) (1), benzo- [1.2-d:4.5-d']bis[1.3]dioxole (2), benzo[1.2-d:3.4-d']bis[1.3]dioxole (3) and benzotris[1.3]dioxole (4) have been measured at room temperature. Hyperfine splitting constants of the aromatic ring protons of the compounds 1 - 3 have been determined. They have been correlated with the HOMO orbital densities of the adjacent carbon atoms and exhibit sufficient correspondence with the reactivities of these compounds in electrophilic substitution reactions. The splitting constants of all protons of the compounds 1 - 4 have been calculated by the INDO and HMO methods and have been compared with the experimental hyperfine values. By perturbation theory applied to the interactions between the π-MO'S of benzene and the dioxole fragment one can explain and understand the magnitudes of the experimental hyperfine splitting constants of the hydrogen atoms of these compounds. In particular, the hyperfine values of the methylene protons calculated by the HMO method are in good agreement with the experimental data.

Lewis-Base Adducts of Lead(II) Compounds. XIII. Synthetic, Structural and Theoretical Studies of Some 2:1 Adducts of 1,10-Phenanthroline With Lead(II) Oxoanion Salts

1996 ◽  
Vol 49 (10) ◽  
pp. 1099 ◽  
Author(s):  
I Bytheway ◽  
LM Engelhardt ◽  
JM Harrowfield ◽  
DL Kepert ◽  
H Miyamae ◽  
...  
Keyword(s):  
Room Temperature ◽  
Electron Pair ◽  
Lone Pair ◽  
Coordination Complexes ◽  
Lewis Base ◽  
Theoretical Studies ◽  
Hydrogen Atoms ◽  
X Ray ◽  
Structure Determinations ◽  
Good Agreement

Syntheses and room-temperature single-crystal X-ray structure determinations are recorded for 2 : 1 adducts of the N,N′- bidentate aromatic base 1,10-phenanthroline (' phen ') with lead(II) nitrate and perchlorate . [( phen )2Pb(NO3)2] is monoclinic, P21/n, a 18.104(4), b 7.733(2), c 16.688(3) Ǻ, β 98.17(2)′, Z = 4, R being 0.036 for No = 3381 independent 'observed' reflections, while [( phen )2Pb(ClO4)2] is triclinic, Pī , a 13.134(4), b 12.342(4), c 7.771(3) Ǻ, α 94.34(3), β 101.49(3), γ 93.91(2)′, Z = 2, R being 0.056 for No 3473. The two systems are mononuclear with eight-coordinate PbN4O4 coordination environments incorporating a pair of O,O'- bidentate anions. Stereochemical calculations, based on valence shell electron pair repulsion (VSEPR) theory, have been performed for coordination complexes of the general type [M( bidentate A)n( bidentate B)4-n] (n = 1 or 2) and for several types of lead(II) complex thought to contain sterically active lone pairs of electrons. Expected deviations from ideal stereochemistry have been successfully predicted and for many of the complexes studied there is good agreement between the observed and calculated stereochemistry. In the particular case of these lead(II)/ phen complexes it appears to be necessary to invoke steric interactions of the a-hydrogen atoms in addition to a sterically active lone pair.

Flame structure and flame reaction kinetics - V. Investigation of reaction mechanism in a rich hydrogen+nitrogen+oxygen flame by solution of conservation equations

1970 ◽  
Vol 317 (1529) ◽  
pp. 235-263 ◽  
Keyword(s):  
Reaction Mechanism ◽  
Hydrogen Atom ◽  
Reaction Zone ◽  
Rate Constant ◽  
Rate Constants ◽  
Time Dependent ◽  
Flame Velocity ◽  
Atom Concentration ◽  
Comparison With Experiment ◽  
Oxygen Flame

A powerful combination of two computational methods has been used to investigate the reaction mechanism in a fuel-rich hydrogen+nitrogen+oxygen flame. The first of these involves the solution of the time-dependent heat conduction and diffusion equations by finite difference methods. It allows a preliminary assessment of reaction mechanisms and rate constants which must be used to reproduce the observed flame velocity. However, the transport fluxes are only represented approximately in this time-dependent model, so that a precise calculation of flame profiles cannot be made. The second computational method uses a Runge–Kutta procedure to calculate the steady-state flame profiles, and is an extension of the methods discussed by Dixon-Lewis (1968). It incorporates detailed transport property calculations, and thus allows computation of detailed flame profiles for comparison with experiment. Application of the methods to the rich hydrogen+nitrogen+oxygen flame and subsequent comparison with experiment has established the participation of hydroperoxyl in the flame mechanism, and has shown the principal reactions in the flame to be: OH + H 2 = H 2 O + H, (i) H + O 2 =OH + O, (ii) O + H 2 =OH + H, (iii) H + O 2 + M = HO 2 + M, (iv) H + HO 2 = OH + OH, (vii) H + HO 2 = H 2 + O 2 , (xii) H+ H + M = H 2 + M. (xv) It was found that the interplay between these reactions is such that it is impossible to use the atmospheric pressure flame for an independent, precise determination of the hydrogenoxygen chain branching-rate constant k 2 . Another property of the mechanism is that the hydrogen atom concentration profile in the flame is not very dependent on the precise rate constants employed, so that the profile itself can be computed probably to better than ±10%. The reaction zone of the very rich flame commences at about 550 K, the maximum overall reaction rate is at about 900 K, and the maximum hydrogen atom concentration is at 1030 to 1040 K. The rate constant ratio k 7 / k 12 is found to lie in the range 5±1, assumed independent of temperature over the reaction zone. Assuming equal efficiencies of all the molecules in the flame as third bodies in the hydrogen atom recombination, the rate constant k 15 is estimated to lie in the range 4.5±1.5 x 10 15 cm 6 mol -2 s -1 .

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