intrinsic barrier
The Gibbs energy of activation (Δ‡G) in the limiting case where ΔG° = 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: \[\Delta ^{\ddagger}G = \frac{\lambda }{4}\]
PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1126 (