Ion transfer across the interface of two immiscible liquids involves a mech
anism for initiating desolvation from the first liquid, A, and concerted so
lvation by the second, B. In the present article a mechanism is considered
in which this initiation is facilitated by the ion attaching itself to the
tip of a solvent protrusion of B into A. (Protrusions have been observed in
computer simulations and termed "fingers" or "cones.") It is presumed that
the most effective protrusion represents a balance between two opposing ef
fects: the more convex the protrusion the less probable the ion/protrusion
formation but also the less the resistance to extrusion of the intervening
liquid between the ion and the surface. An analogy of the latter to hydrody
namics is noted, namely, the more convex the surface the less the frictiona
l force it exerts on the approaching ion. After diffusion in coordinate and
solvation space across the interfacial region, the final detachment of the
ion from solvent A is assumed to occur from a protrusion of A into B. Exis
ting data on ion transfer rates are discussed, including the question of di
ffusion vs kinetic control. Computer simulations that correspond to the exp
erimental conditions in realistic liquids for measurement of the electroche
mical exchange current rate constant k(0) are suggested. They can be used t
o test specific theoretical features. With a suitable choice of systems the
need (and a major barrier to the simulations) for having a base electrolyt
e in such simulations can be bypassed. An experiment for the real-time obse
rvation of an ion leaving the interface is also suggested. (C) 2000 America
n Institute of Physics. [S0021-9606(00)50628-X].