Rice-Ramsperger-Kassel Marcus

In the statistical description of ununolecular kinetics, known as Rice-Ramsperger-Kassel-Marcus (RRKM) theory [4,7,8], it is assumed that complete IVR occurs on a timescale much shorter than that for the unimolecular reaction [9]. Furdiemiore, to identify states of the system as those for the reactant, a dividing surface [10], called a transition state, is placed at the potential energy barrier region of the potential energy surface. The assumption implicit m RRKM theory is described in the next section. 

Klippenstein S J 1992 Variational optimizations in the Rice-Ramsperger-Kassel-Marcus theory calculations for unimolecular dissociations with no reverse barrier J. Chem. Rhys. 96 367-71... 

Marcus developed a quantum mechanical formulation of Kassel-Rice-Ramsperger theories in which zero point energies have been taken into account (see flow chart). However, due to lack of data for individual molecules it is difficult to apply the theory of Rice-Ramsperger-Kassel-Marcus (RRKM)... 

For the rigid entrance/rigid exit complex-forming bimolecular reaction HO + CO — H + CO2, which passes through HOCO, a separated-step conventional Rice-Ramsperger-Kassel-Marcus (RRKM) treatment extremely well reproduces the experimental temperature and pressure dependences of this four-atom system. 

Marcus is a coauthor of the Rice-Ramsperger-Kassel-Marcus theory of molecular reactions. However, his theoretical work in the 1950s on electron transfer reactions started him on his pathway to eminence. Back then, chemists knew electron-transfer processes were occurring during chemical reactions, but they had no way to predict the speed of a reaction or to develop strategic chemical experiments. In addition, some reactions that were predicted to proceed rapidly instead poked along at a snail s pace. 

In more detail, our approach can be briefly summarized as follows gas-phase reactions, surface structures, and gas-surface reactions are treated at an ab initio level, using either cluster or periodic (plane-wave) calculations for surface structures, when appropriate. The results of these calculations are used to calculate reaction rate constants within the transition state (TS) or Rice-Ramsperger-Kassel-Marcus (RRKM) theory for bimolecular gas-phase reactions or unimolecular and surface reactions, respectively. The structure and energy characteristics of various surface groups can also be extracted from the results of ab initio calculations. Based on these results, a chemical mechanism can be constructed for both gas-phase reactions and surface growth. The film growth process is modeled within the kinetic Monte Carlo (KMC) approach, which provides an effective separation of fast and slow processes on an atomistic scale. The results of Monte Carlo (MC) simulations can be used in kinetic modeling based on formal chemical kinetics. 

Nowadays, the basic framework of our understanding of elementary processes is the transition state or activated complex theory. Formulations of this theory may be found in refs. 1—13. Recent achievements have been the Rice—Ramsperger—Kassel—Marcus (RRKM) theory of unimol-ecular reactions (see, for example, ref. 14 and Chap. 4 of this volume) and the so-called thermochemical kinetics developed by Benson and co-workers [15] for estimating thermodynamic and kinetic parameters of gas phase reactions. Computers are used in the theory of elementary processes for quantum mechanical and statistical mechanical computations. However, this theme will not be discussed further here. 

More sophisticated treatments of Lindemann s scheme by Lindemann— Hinshelwood, Rice—Ramsperger—Kassel (RRK) and finally Rice— Ramsperger—Kassel—Marcus (RRKM) have essentially been aimed at re-interpreting rate coefficients of the Lindemann scheme. RRK(M) theories are extensively used for interpreting very-low-pressure pyrolysis experiments [62, 63]. 

Theoretical Expressions. The Rice-Ramsperger-Kassel-Marcus (RRKM14) theory of unimolecular reactions employs a quantum statis-... 

RRKM Rice-Ramsperger-Kassel-Marcus [theory]... 

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