Unimolecular Decomposition and Some Isotope Effects of Simple Alkanes and Alkyl Radicals

Rabinovitch, B. S.; Setser, D. W.

doi:10.1002/9780470133330.ch1

Cited by 190 publications

(3 citation statements)

References 79 publications

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“…More detailed treatments of the deactivation rate are possible (46). The rate constant ka was evaluated using a standard program by Hase and Bunker (47), with the density of states N*(E*) evaluated by the Whitten-Rabinovitch semiclassical method (48), and the sum of states W(E t) evaluated by direct count (49). The partition functions were calculated as discussed in Ref.…”

Section: W(e~) = ~ P(evr ~)mentioning

confidence: 99%

A Mathematical Model of the Fluid Mechanics and Gas‐Phase Chemistry in a Rotating Disk Chemical Vapor Deposition Reactor

Coltrin

Kee

Evans

1989

J. Electrochem. Soc.

251

159

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We describe a mathematical model of the coupled fluid mechanics and gas‐phase chemical kinetics in a rotating disk chemical vapor deposition reactor. The analysis is for the flow between an infinite radius, heated nonporous rotating disk and a parallel infinite radius porous surface through which reactive fluid is injected normal to the disk. The analysis extends the usual von Karman transformation to allow specification of the normal velocity at the porous disk, and reduces to a stagnation point flow in the limit of zero rotating rate. The deposition of silicon from silane is used as an example system. A new reaction mechanism and set of rate constants are given for the thermal decomposition of silane. We present an RRKM analysis of several of the unimolecular reactions in the mechanism. Calculated velocity and temperature profiles, chemical species density profiles, and deposition rates as functions of susceptor temperature, spin rate, and inlet flow velocity are presented.

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Section: W(e~) = ~ P(evr ~)mentioning

confidence: 99%

A Mathematical Model of the Fluid Mechanics and Gas‐Phase Chemistry in a Rotating Disk Chemical Vapor Deposition Reactor

Coltrin

Kee

Evans

1989

J. Electrochem. Soc.

251

159

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“…This rate constant is defined as where D is the probability of forming the decomposition products and S is the probability of forming collisionally stabilized reactant. With the RRKM model of a time-independent unimolecular rate constant for a monoenergetically excited reactant, k (ω, E ) is pressure, i.e., ω, independent and equals the RRKM rate constant k ( E ).…”

Section: Introductionmentioning

confidence: 99%

Unimolecular Rate Constants versus Energy and Pressure as a Convolution of Unimolecular Lifetime and Collisional Deactivation Probabilities. Analyses of Intrinsic Non-RRKM Dynamics

Malpathak

Hase

2019

J. Phys. Chem. A

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Following work by Slater and Bunker, the unimolecular rate constant versus collision frequency, k uni (ω,E), is expressed as a convolution of unimolecular lifetime and collisional deactivation probabilities. This allows incorporation of nonexponential, intrinsically non-RRKM, populations of dissociating molecules versus time, N(t)/N(0), in the expression for k uni (ω,E). Previous work using this approach is reviewed. In the work presented here, the biexponentialand f 1 + f 2 = 1. With these two constraints, there are two adjustable parameters in the biexponential N(t)/N(0) to represent intrinsic non-RRKM dynamics. The rate constant k 1 is larger than k(E) and k 2 is smaller. This biexponential gives k uni (ω,E) rate constants that are lower than the RRKM prediction, except at the high and low pressure limits. The deviation from the RRKM prediction increases as f 1 is made smaller and k 1 made larger. Of considerable interest is the finding that, if the collision frequency ω for the RRKM plot of k uni (ω,E) versus ω is multiplied by an energy transfer efficiency factor β c , the RRKM k uni (ω,E) versus ω plot may be scaled to match those for the intrinsic non-RRKM, biexponential N(t)/N(0), plots. This analysis identifies the importance of determining accurate collisional intermolecular energy transfer (IET) efficiencies.

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“…This can be accounted for with variable transition-state theory Sølling et al, 2011), and preliminary calculations indicate that the reversal of the secondary isotope effect can be described in a similar manner. It was originally suggested that this phenomenon would be the result of a statistical weight effect (Rabinovitch, Setser, & Schneider, 1961;Rabinovitch & Setser, 1964;Watkins & O'Deen, 1971;Ingemann et al, 1989Ingemann et al, , 1988bIngemann et al, , 1991 involving hypothesized weakening of high-energy vibrations that would particularly influence the transition state sum of states of high-internal-energy reactants.…”

Section: S C H E M E 16mentioning

confidence: 99%

Secondary kinetic deuterium isotope effects on unimolecular cleavage reactions: Zero‐point vibrational energy and qualitative RRKM theory

Østergaard

Hammerum

2021

Mass Spectrometry Reviews

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Secondary kinetic isotope effects arise as the result of transition-state zeropoint vibrational energy differences. Unimolecular simple cleavage reactions of gas-phase ions in mass spectrometers allow detailed studies of isotope effects on competing reactions, particularly when examined in intramolecular competition experiments where interpretation requires very few simplifying assumptions. The zero-point energy differences reflect changes of isotope sensitive vibrational properties, and both αand β-secondary deuterium isotope effects are related to the sp 3 → sp 2 hybridization changes that accompany bond cleavage. Deuterium substitution three bonds or more removed from the bond broken also gives rise to isotope effects, but their origin is less easily interpreted. The magnitude and variation of the observed effects depend not only on zero-point energy differences; a number of additional factors play a role. The influence of the critical energy, the excess energy, the size of the reactant, and the presence of competing reactions can be rationalized within a simple, qualitative RRKM framework. The distinction between kinetic and thermodynamic isotope effects is not always obvious.

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Unimolecular Decomposition and Some Isotope Effects of Simple Alkanes and Alkyl Radicals

Cited by 190 publications

References 79 publications

A Mathematical Model of the Fluid Mechanics and Gas‐Phase Chemistry in a Rotating Disk Chemical Vapor Deposition Reactor

A Mathematical Model of the Fluid Mechanics and Gas‐Phase Chemistry in a Rotating Disk Chemical Vapor Deposition Reactor

Unimolecular Rate Constants versus Energy and Pressure as a Convolution of Unimolecular Lifetime and Collisional Deactivation Probabilities. Analyses of Intrinsic Non-RRKM Dynamics

Secondary kinetic deuterium isotope effects on unimolecular cleavage reactions: Zero‐point vibrational energy and qualitative RRKM theory

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