  In the pioneering work by R. A. Marcus, the solvation effect on electron
transfer (ET) processes was investigated, giving rise to the celebrated
nonadiabatic ET rate formula. In this work, on the basis of the thermodynamic
solvation potentials analysis, we reexamine Marcus' formula with respect to the
Rice-Ramsperger-Kassel-Marcus (RRKM) theory. Interestingly, the obtained RRKM
analogue, which recovers the original Marcus' rate that is in a linear
solvation scenario, is also applicable to the nonlinear solvation scenarios,
where the multiple curve{crossing of solvation potentials exists. Parallelly,
we revisit the corresponding Fermi's golden rule results, with some critical
comments against the RRKM analogue proposed in this work. For illustration, we
consider the quadratic solvation scenarios, on the basis of physically
well-supported descriptors.
