Reactions of hot hydrogen atoms in mercaptan–ethylene systems

1968 ◽  
Vol 46 (17) ◽  
pp. 2878-2880 ◽  
Author(s):  
R. P. Steer ◽  
A. R. Knight
Keyword(s):  
Rate Constant ◽  
Inert Gas ◽  
Primary Process ◽  
Process Rate ◽  
Hydrogen Atoms ◽  
Process Rate Constant

Investigation of the photolysis of methanethiol and ethanethiol vapor in the presence of ethylene and inert gas has indicated the formation of energetic hydrogen atoms in the primary process. Rate constant ratios for the reactions of these species have been found to be pressure dependent.

The reaction of hydrogen atoms with propylene

1971 ◽  
Vol 324 (1559) ◽  
pp. 433-446 ◽  
Keyword(s):  
Rate Constant ◽  
Rate Constants ◽  
Flow System ◽  
Primary Process ◽  
Absolute Rate ◽  
Hydrogen Atoms ◽  
Vibrationally Excited ◽  
Flow Rates ◽  
Detailed Mechanism ◽  
Excited Species

A detailed study has been made of the products of the reaction of hydrogen atoms with propylene. A discharge-flow system at 290±3 K was used. Total pressures in the range 4 to 16 Torr (550 to 2200 N m -2 ) of argon were used and the flow rates of hydrogen atoms and propylene ranged individually up to about 12 μ mol s -1 . As found by others the main products are methane, ethane, ethylene, propane and isobutane. Trivial amounts of 2,3-dimethylbutane, but no n-butane, were detected. A detailed mechanism accounting adequately for the reaction is proposed. It is confirmed that formation of the vibrationally excited species, i-C 3 H 7 *, is the predominant primary process. Novel processes which are shown to be important are H+i-C 3 H 7 * → CH 3 +C 2 H 5 and, C 3 H 8 * → CH 4 +C 2 H 4 . A number of rate constant ratios have been evaluated from the data and these allow calculation of absolute rate constants of some individual reactions. The agreement with previously reported values is, in most instances, good.

The possibility of investigating saturation processes using a generalized expression of the process rate constant

1990 ◽  
Vol 26 (5) ◽  
pp. 495-498 ◽  
Author(s):  
Z. Kubaitis ◽  
A. Jurevichiute ◽  
A.E. Chalykh
Keyword(s):  
Rate Constant ◽  
Process Rate ◽  
Process Rate Constant

Reactions of thiyl radicals. VI. Photolysis of ethanethiol

1969 ◽  
Vol 47 (8) ◽  
pp. 1335-1345 ◽  
Author(s):  
R. P. Steer ◽  
A. R. Knight
Keyword(s):  
Bond Cleavage ◽  
Addition Product ◽  
Inert Gas ◽  
Effect Of Temperature ◽  
Primary Process ◽  
Hydrogen Atoms ◽  
Diethyl Sulfide ◽  
Rate Constant Ratio ◽  
Olefinic Double Bond ◽  
A Chain

The photolysis of ethanethiol vapor in the pressure range 10 to 350 Torr and the effect of % decomposition, wavelength, and of added inert gas and ethylene on the rate of formation of the products has been determined. In addition, the effect of temperature on the photolysis of methanethiol–ethylene–inert gas and ethanethiol–ethylene–inert gas systems has been studied.For the pure substrate, the primary process is S—H bond cleavage and the hydrogen atom produced abstracts the sulfyhydryl hydrogen of the substrate. The quantum yield of molecular hydrogen formation is unity, independent of pressure. C2H5S radicals, formed either in the primary process or as a result of abstractive attack by H atoms or radicals on the substrate, combine to form an excited disulfide molecule. The major condensable product, C2H5SSC2H5, arises via collisional deactivation of this excited species which can also sensitize the decomposition of the substrate to give C2H4, C2H6, and H2S, the other products observed. With added inert gas the rates of formation of the minor products decrease whereas hydrogen and disulfide remain unchanged.With added ethylene, the major products are H2, C2H5SSC2H5, and C2H5SC2H5, the addition product. Diethyl sulfide is formed in a chain reaction by the attack of C2H5S on the olefinic double bond to form the composite radical, followed by H abstraction from the substrate. The hydrogen rate decreases due to the addition of H atoms to ethylene. The rate constant ratio, k22/k4, for the reactions [22] and [4], respectively,[Formula: see text]is pressure dependent, indicative of the formation of hot hydrogen atoms in the primary process of the photolysis of methanethiol and ethanethiol. The Arrhenius parameters A22/A4 and E22−E4 for the methanethiol–ethylene and ethanethiol–ethylene systems have been determined. Kinetic treatments of the proposed mechanisms have been undertaken.

Hg(63P1)-sensitized decomposition of HNCO vapor and HNCO–H2 mixtures; the reaction of hydrogen atoms with HNCO

1968 ◽  
Vol 46 (4) ◽  
pp. 527-530 ◽  
Author(s):  
N. J. Friswell ◽  
R. A. Back
Keyword(s):  
Quantum Yield ◽  
Cross Section ◽  
Initial Step ◽  
Primary Process ◽  
Hydrogen Atoms ◽  
Direct Photolysis ◽  
A Value ◽  
The Cross

The Hg(63P1)-sensitized decomposition of HNCO vapor has been briefly studied at 26 °C with HNCO pressures from about 3 to 30 Torr. The products detected were the same as in the direct photolysis, CO, N2, and H2. The quantum yield of CO was appreciably less than unity, compared with a value of 1.5 in the direct photolysis under similar conditions. From this and other observations it is tentatively concluded that a single primary process occurs:[Formula: see text]From a study of the mercury-photosensitized reactions in mixtures of HNCO with H2, it was concluded that hydrogen atoms react with HNCO to form CO but not N2. The initial step is probably addition to form NH2CO. From the competition between reaction [1] and the corresponding quenching by H2, the cross section for reaction [1] was estimated to be 2.3 times that of hydrogen.

Reactions of hydrogen atoms with hexafluoroacetone

1978 ◽  
Vol 56 (20) ◽  
pp. 2638-2645 ◽  
Author(s):  
D. W. Grattan ◽  
K. O. Kutschke
Keyword(s):  
Rate Constant ◽  
Cross Sections ◽  
The Other ◽  
Hydrogen Atoms ◽  
Kinetics Of

Attempts were made to study the kinetics of the reaction of atomic H with (CF3)2CO vapour (HFA). Atomic H was generated from H2 by mercury photosensitization in the presence of C2H4 and HFA but the system was complicated by the loss of C2H5 radicals by addition to HFA and the kinetic results were intractable. When atomic H was generated from C3H8, the kinetics again were obscured by some unidentified reaction(s) which became more important at higher [HFA]/[C3H8]. An estimate of the rate constant for the addition of H to HFA obtained at low [HFA]/[C3H8] yielded k9 = 8.5 × 105 l mol−1 s−1. Trifluoroacetaldehyde was identified with some reliability but many of the other heavier products formed in the H2 + HFA reaction could not be identified. Quenching cross-sections were determined for C2H4, C3H8, C4H10, and HFA relative to that for N2O.

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.

Curve-crossing collisions of excited lead atoms in flames

1981 ◽  
Vol 376 (1767) ◽  
pp. 545-564 ◽  
Keyword(s):  
Rate Constant ◽  
Atomic Hydrogen ◽  
Negative Temperature Coefficient ◽  
Negative Temperature ◽  
Model Systems ◽  
Attractive Potential ◽  
Hydrogen Atoms ◽  
Lennard Jones ◽  
Increasing Temperature ◽  
Curve Crossing

Lead atoms, present as a trace additive in a series of premixed H 2 –N 2 –O 2 flames, were excited to the 7 3 P o 1 state by 405.8 nm radiation from a nitrogen-pumped dye laser. Rate constants for spin-orbit relaxation to the 7 3 P o 0 state were obtained separately for collisions with atomic hydrogen and for collisions with the bulk flame gas, by measuring the relative intensities of fluorescence at 364.0 and 368.3 nm as a function of distance from the reaction zone in each flame. For hydrogen atoms the rate constant is typically 1 x 10 -9 cm 3 molecule -1 s -1 , decreasing with increasing temperature; for the bulk flame gas the rate constant is typically 1 x 10 -11 cm 3 molecule -1 s -1 , increasing with increasing temperature. Numerical calculations for model systems, with the use of Morse and Lennard-Jones potentials to describe the interaction of the colliding species, show that the negative temperature coefficient found for atomic hydrogen can be attributed to the crossing of attractive potential curves, corresponding to bound excited states of PbH.

Shock-wave observations of rate constants for atomic hydrogen recombination from 2500 to 7000 °K: collisional stabilization by exchange of hydrogen atoms

1969 ◽  
Vol 310 (1501) ◽  
pp. 253-276 ◽  
Keyword(s):  
Shock Waves ◽  
Rate Constant ◽  
Rate Constants ◽  
Atomic Hydrogen ◽  
Functional Form ◽  
Kcal Mole ◽  
Hydrogen Atoms ◽  
Hydrogen Molecules ◽  
Hydrogen Recombination ◽  
Equilibrium Dissociation

Rate constants for the recombination of atomic hydrogen with hydrogen molecules, hydrogen atoms, and argon atoms as the third bodies are presented in functional form for the range of temperatures from about 2500 to 7000 °K and are critically compared with the results of other workers. The rate constants are evaluated from detailed analyses of spectrum-line reversal measurements of the fall in temperature accompanying dissociation behind shock waves in gas mixtures containing 20, 40, 50 and 60% of hydrogen in argon. The rate constants for recombination with hydrogen molecules ( k -1 ) and argon atoms ( k -3 ) fit the equations log 10 k -1 = 15.243 - 1.95 x 10 -4 T cm 6 mole -2 s -1 , log 10 k -3 = 15.787 - 2.75 x 10 -4 T cm 6 mole -2 s -1 , with a standard deviation of 0.193 in log 10 k -1 . The rate constant for recombination with hydrogen atoms is about ten times larger than these at 3000 °K and shows a steep inverse dependence on temperature ( ~ T -6 ) above 4000 °K. Below this temperature the power of this dependence decreases rapidly and there is strong evidence that the value of this rate constant has a maximum around 3000 °K. This behaviour is interpreted on the basis of a process of collisional stabilization by atom exchange, requiring an activation energy around 8 kcal mole -1 and taking place under conditions of vibrational adiabaticity. The over-all results indicate that the assumption of equality between the equilibrium constant and the ratio of the rate constants for dissociation and recombination is valid throughout the region of non-equilibrium dissociation and at all temperatures in the shock waves examined.

Kinetics of the reaction H + C2H6 → H2 + C2H5 in the temperature region of 1000 K

1984 ◽  
Vol 62 (1) ◽  
pp. 86-91 ◽  
Author(s):  
J.-R. Cao ◽  
M. H. Back
Keyword(s):  
Equilibrium Constant ◽  
Rate Constant ◽  
Temperature Region ◽  
Recent Measurement ◽  
Hydrogen Atoms ◽  
Elementary Reactions ◽  
Temperature Range ◽  
Hydrogen Molecules ◽  
Kinetics Of ◽  
Rate Controlling Step

A system for the measurement of rate constants for elementary reactions of hydrogen atoms in the temperature region of 1000 K is described. The concentration of hydrogen atoms is controlled by the equilibrium constant for dissociation of hydrogen molecules. The kinetics of the rate of conversion of ethane to ethylene in this system has been studied over the temperature range 876–1016 K. The results show that the rate-controlling step is[Formula: see text]and the value obtained for the rate constant is[Formula: see text](R = 1.987 cal mol−1 deg−1). This value is compared with values obtained from other methods over the temperature range 300–1400 K. Combination with a recent measurement of the rate constant for the reverse reaction yields an experimental value for the equilibrium constant for the reaction.

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