The Gibbs energy of activation (\(\Delta ^{\ddagger}G\)) in the limiting case where \(\Delta G^{\,\unicode{x26ac}} = 0\), 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, \(\lambda \), of the reaction by the equation: \[\Delta ^{\ddagger}G = \frac{\lambda }{4}\]