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Marcus–Hush relationship

Relationship between the barrier (Δ G ‡) to thermal electron transfer, the energy of a corresponding optical charge-transfer transition (Δ E op), and the overall change in standard Gibbs energy accompanying thermal electron transfer (Δ G o). Assuming a quadratic relation between the energy of the system and its distortions from equilibrium (harmonic oscillator model) the expression obtained is:
Δ G ‡ = Δ E op 2 4 ( Δ E op − Δ G o )
The simplest form of this expression obtains for degenerate electron transfer (Δ G o) in e.g. symmetrical mixed valence systems:
Δ G ‡ = Δ E op 4
Note that for this situation the Marcus equation reads:
Δ G ‡ = λ 4
Source:
PAC, 1996, 68, 2223 (Glossary of terms used in photochemistry (IUPAC Recommendations 1996)) on page 2253
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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. ISBN 0-9678550-9-8. doi:10.1351/goldbook.
Last update: 2014-02-24; version: 2.3.3.
DOI of this term: doi:10.1351/goldbook.M03703.
Original PDF version: http://www.iupac.org/goldbook/M03703.pdf. The PDF version is out of date and is provided for reference purposes only. For some entries, the PDF version may be unavailable.
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