Kinetics of the Homogeneous Exchange Reaction: NH3 +D2→NH2D +HD. Single-Pulse Shock-Tube Studies

Schechner, Pinhas; Burcat, Alexander; Lifshitz, Assa

doi:10.1063/1.1672688

Cited by 5 publications

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References 14 publications

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“…8 discussed above, shows that no serious fallacy is introduced by assuming equilibrium population distributions, at least as far as the overall rate is concerned. Thus, with X = H and Y = D, reactions [7] and [8] are many orders of magnitude too slow to give the experimentally observed rates of equilibration of H2 and D,, as has been pointed out several times (6,7,15,18). One is therefore left with the paradox that although most theoretical predictions put the activation energy barrier for the molecular exchange [9] very high indeed (19)(20)(21)(22), that reaction would have to be very fast indeed to account for the observed rates (6,15,16,23).…”

Section: Resultsmentioning

confidence: 99%

The Master Equation for the Dissociation of a Dilute Diatomic Gas. VI. Solution of Coupled Sets of Master Equations

McElwain¹,

Pritchard²

1972

Can. J. Chem.

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Three coupled sets of master equations, representing the equilibration of X, + Y , e 2XY via atoms only, have been solved by the normal-mode technique; the set of 57 simultaneous differential equations describing the H2/D,/2HD system was considered as a suitable trial model. It was found that at times ( t ) in excess of the longest vibrational relaxation time, even though some of the populations in the system appeared highly nonBoltzmann, all the phenomenological rate constants were well-behaved: they were either constant and obeyed the rate-quotient law, or they were dependent on t2.The paper concludes with a discussion of the information required before a full solution of the X, + Y+ F! 2XY reaction could be contemplated, and suggests methods by which an approximation to such a solut~on could be obtained. IntroductionEarlier papers in this series (1-5) have been concerned with the dissociation and recombination of a homonuclear diatomic gas at infinite dilution in a bath of rozully inert atoms, and at such temperatures that rotational equilibration can be considered infinitely rapid.' In most of this work, the H, molecule has been used as a model, and having only 15 vibrational levels, can be represented by a set of 16 simultaneous differential equations; Part V addressed itself to the problem having a rather more dense energy-level spectrum, using D, as a model, and giving rise to a master equation of order 23. It is hoped that in future work, a more realistic description of the dissociation and recombination of a dilute homonuclear diatomic gas can be achieved by considering both rotational and vibrational interchanges; it should be mentioned in passing that for H,, this will require the solution of almost 400 simultaneous differential equations and the assignment of some 70 000 translational-vibrational transition probabilities; for D, the problem is even more forbidding,

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Section: Resultsmentioning

confidence: 99%

The Master Equation for the Dissociation of a Dilute Diatomic Gas. VI. Solution of Coupled Sets of Master Equations

McElwain¹,

Pritchard²

1972

Can. J. Chem.

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The homogeneous reaction CD₄ + NH₃ → CD₃H + NH₂D: The effect of ethane impurities

Lifshitz¹,

Schechner²

1975

Int J of Chemical Kinetics

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The homogeneous exchange reaction between tetradeutero methane and ammonia was studied behind reflected shocks in a single-pulse shock tube over the temperature range of 1300-1800°K. The rate of production of CD3H at the early stages of the reaction in mixtures ranging between 1-4.5y0 NH3 and l--4.3yO CD4 in argon is given by d]o, where ka = 8 X 10'6 exp (-65.3 X lO3/RT) cm3/mole.sec. This activation energy is considerably lower than the one that may be expected on the basis of a pure free radical mechanism. It is rationalized by CtDs impurities in the methane. No clear answer can be obtained regarding the role of a four-center intermediate in this reaction.* This work was abstracted from the dissertation of P. S., submitted to the Senate of Hebrew University in partial fulfillment of the requirements for the Ph.D. degree.

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Homogeneous Exchange Reaction: CD4+CH4→CD3H+CH3D. Single Pulse Shock Tube Studies

Burcat¹

1970

The Journal of Chemical Physics

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The homogeneous exchange reaction between CH4 and CD4 was investigated using the single pulse shock tube technique. The temperature range covered was 1340–1745°, and concentrations up to 8% total methane in argon were used. The over-all rate of exchange is proportional to the 32 power of the methane concentration and is independent of the argon density. The rate of exchange in mixtures containing 4% CH4 + 1% CD4 and 4% CD4 + 1% CH4 was found to be the same, indicating a negligible isotope effect at the temperature range covered in this study. For mixtures in which [CH4] = [CD4] the rate of exchange is given by d[CD3H] / dt = kr[CH4]0.75[CD4]0.75, where kr = 4.3 × 1014exp[−(70 ± 2) × 103 / RT]cc0.5mole−0.5·sec−1. It was shown that the exchange proceeds via a chain reaction mechanism carried by CH3 and CD3 free radicals. The evaluated rate constants for the chain, CH3+CD4→ lim k3CD3+CH3D, CD3+CH4→ lim k4CH3+CD3H, are by a factor of 10 higher than the ones extrapolated from the low temperature studies on the basis of an Arrhenius plot.

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Kinetics of the Homogeneous Exchange Reaction: NH3 +D2→NH2D +HD. Single-Pulse Shock-Tube Studies

Cited by 5 publications

References 14 publications

The Master Equation for the Dissociation of a Dilute Diatomic Gas. VI. Solution of Coupled Sets of Master Equations

The Master Equation for the Dissociation of a Dilute Diatomic Gas. VI. Solution of Coupled Sets of Master Equations

The homogeneous reaction CD₄ + NH₃ → CD₃H + NH₂D: The effect of ethane impurities

Homogeneous Exchange Reaction: CD4+CH4→CD3H+CH3D. Single Pulse Shock Tube Studies

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Kinetics of the Homogeneous Exchange Reaction: NH3 +D2→NH2D +HD. Single-Pulse Shock-Tube Studies

Cited by 5 publications

References 14 publications

The Master Equation for the Dissociation of a Dilute Diatomic Gas. VI. Solution of Coupled Sets of Master Equations

The Master Equation for the Dissociation of a Dilute Diatomic Gas. VI. Solution of Coupled Sets of Master Equations

The homogeneous reaction CD4 + NH3 → CD3H + NH2D: The effect of ethane impurities

Homogeneous Exchange Reaction: CD4+CH4→CD3H+CH3D. Single Pulse Shock Tube Studies

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The homogeneous reaction CD₄ + NH₃ → CD₃H + NH₂D: The effect of ethane impurities