Rice-Ramsperger-Kassel theory

Rabinovitch et al. (85) studied the reaction of H atoms with trans-ethylene-d2 as a function of ethylene pressure in the temperature range — 78 to 160°C. They were able to account for all secondary reactions of the hot ethyl radicals and to determine the rates of their decomposition (relative to stablization). Simultaneously they calculated the theoretical rates on the basis of the Rice-Ramsperger-Kassel theory of uni-molecular reactions, using expressions derived by Marcus (71), and found a reasonable agreement with the experimental values. Similar satisfactory agreements had been found previously by Rabinovitch and Die-sen (84) for hot sec-butyl radicals. Extensive studies of hot radicals produced by H or D atom additions to various olefins have been carried... 

When the system is not in thermal equilibrium, the use of thermodynamic relationships like equations (5) and (6) would not be rigorous. However, it has been shown that these equations can be derived from RRK (Rice-Ramsperger-Kassel) theory without assuming thermal equilibrium for the system. Furthermore,... 

The lower activation energy found at these high temperatures was explained by Schott and Davidson in terms of the Rice-Ramsperger-Kassel theory. 

Rice-Ramsperger-Kassel) theory/ giving activation energies of 1.0-1.5 eV, but entropic effects were not considered in this analysis. 

This chapter is devoted to the presentation of the computational methods used for the determination of the thermodynamic and the kinetic data of the compound considered in this work. We give in a first part a theoretical background of the methods used in the present work Electronic Structure Theory (ah initio, and Density Functional Theory), Statistical Mechanics theory. Group Additivity method, and multifrequency Quantum Rice-Ramsperger-Kassel theory (QRRK). 

The existence of the polyad number as a bottleneck to energy flow on short time scales is potentially important for efforts to control molecnlar reactivity rising advanced laser techniqnes, discussed below in section Al.2.20. Efforts at control seek to intervene in the molecnlar dynamics to prevent the effects of widespread vibrational energy flow, the presence of which is one of the key assumptions of Rice-Ramsperger-Kassel-Marcns (RRKM) and other theories of reaction dynamics [6]. 

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)... 

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. 

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