A harpoon reaction is a type of chemical reaction, first proposed by Michael Polanyi in 1920,[1][2] whose mechanism (also called the harpooning mechanism) involves two neutral reactants undergoing an electron transfer over a relatively long distance to form ions that then attract each other closer together.
The main feature of these redox reactions is that, unlike most reactions, they have steric factors greater than unity; that is, they take place faster than predicted by collision theory.
Harpoon reactions usually take place in the gas phase, but they are also possible in condensed media.
[4][5] The predicted rate constant can be improved by using a better estimation of the steric factor.
A rough approximation is that the largest separation Rx at which charge transfer can take place on energetic grounds, can be estimated from the solution of the following equation that determines the largest distance at which the Coulombic attraction between the two oppositely charged ions is sufficient to provide the energy