Electron transfer in supercritical carbon dioxide: ultraexothermic charge recombination at the end of the "inverted region".
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.
Serpa
Carlos
C
Departamento de Química, Universidade de Coimbra, 3004-535 Coimbra, Portugal.
Gomes
Paulo J S
PJ
Arnaut
Luis G
LG
Formosinho
Sebastião J
SJ
Pina
João
J
de Melo
J Seixas
JS