intrinsic barrier

The Gibbs energy of activation( $Δ ‡ G$ ) in the limiting case where $Δ G ° = 0$ , i.e. when the effect of thermodynamic driving force is eliminated. According to the Marcus equation, the intrinsic barrier is related to the reorganization energy, $λ$ , of the reaction by the equation:

$Δ ‡ G = λ 4$

Source:

PAC, 1994, 66, 1077 (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1126