Electron transfer in supercritical carbon dioxide: ultraexothermic charge recombination at the end of the "inverted region"

Carlos Serpa; Paulo J S Gomes; Luis G Arnaut; Sebastião J Formosinho; João Pina; J Seixas de Melo

doi:10.1002/chem.200500727

Electron transfer in supercritical carbon dioxide: ultraexothermic charge recombination at the end of the "inverted region"

Chemistry. 2006 Jun 23;12(19):5014-23. doi: 10.1002/chem.200500727.

Authors

Carlos Serpa¹, Paulo J S Gomes, Luis G Arnaut, Sebastião J Formosinho, João Pina, J Seixas de Melo

Affiliation

¹ Departamento de Química, Universidade de Coimbra, 3004-535 Coimbra, Portugal.

PMID: 16548016
DOI: 10.1002/chem.200500727

Abstract

Charge-recombination rates in contact radical-ion pairs, formed between aromatic hydrocarbons and nitriles in supercritical CO(2) and heptane, decrease with the exothermicity of the reactions until they reach -70 kcal mol(-1), but from there on an increase is observed. The first decrease in rate is typical of the "inverted region" of electron-transfer reactions. The change to an increase in the rate for ultra-exothermic electron transfer indicates a new free-energy relationship. We show that the resulting "double-inverted region" is not due to a change in mechanism. It is an intrinsic property of electron-transfer reactions, and it is due to the increase of the reorganisation energy with the reaction exothermicity.