Rice-Ramsperger-Kassel-Marcus (RRKM) theory

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Rice-Ramsperger-Kassel-Marcus (RRKM) theory (RRKM)
Statistical theory of unimolecular reaction rates of gas-phase molecular species that removes most of the simplifying assumptions in the Rice-Ramsperger-Kassel (RRK) theory. Account is taken of the way in which the different normal-mode vibrations and rotations contribute to reaction, and allowance is made for the zero-point energies. The total internal energy is partitioned into active and inactive components, such that only the active component can flow freely among the internal modes and thus contribute to reaction. The assumed equilibrium ratio of active-to-inactive components is evaluated using partition functions. In applications where gas-phase collisions are important, the rates of activation and deactivation take into account their energy dependence, and in the high-pressure limit the transition state is in equilibrium with non-activated reactants and RRKM reduces to conventional transition-state theory.
Note: The theory is also used (with some modification) for reactions in condensed phases.
Related Term(s):

Revised from

IUPAC. Compendium of Chemical Terminology, 2nd ed. (the Gold Book). Compiled by A. D. McNaught and A.Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins.

using additional information from

R. A. Marcus, O. K. Rice. J. Phys. Colloid Chem. 55, 894 (1951).

R. A. Marcus. J. Chem. Phys. 20, 359 (1952). (http://dx.doi.org/10.1063/1.1700424 )

S. C. Tucker. Theor. Chem. Acc. 103, 209 (2000). (http://dx.doi.org/10.1007/s002149900074 )

From Definitions of Terms Relating to Mass Spectrometry (IUPAC Recommendations 2013); DOI: 10.1351/PAC-REC-06-04-06 © IUPAC 2013.

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