# What is a dry electron?

I was reading about water photolysis which produces a positive water radical and a dry electron, or an excited water $\ce{H2O^*}$ through the following equation

$$\ce{ H2O ->[hv] H2O^{.+} + e_{dry}^-, or~ H2O^* }$$ (as seen in this link)

By opposition I have also seen $\ce{e_{aq}^-}$ (as seen in pp. 2 of this link).

I can understand the "positive water" and even the "excited water", but what is a "dry electron"? And what is an $\ce{e_{aq}^-}$ (wet electron? I am unsure of how to translate the term I had learned to english). Why not simply say "free electron"?

• There are a zillion hits on a google search. It is evidently an electron that retains some of the kinetic energy from whatever interaction created the free electron. books.google.com/…
– MaxW
Dec 16 '15 at 16:50
• @MaxW that doesn't explain the term "dry" which is the focus of my question. By opposition I suppose there is also the $e_{aq}^{-}$ ? (adding this to the question) Example on pp 2 in www3.nd.edu/~ndrlrcdc/Compilations/rxn.pdf
– Sos
Dec 17 '15 at 15:03
• $e_{aq}^-$ is quite a natural thing; that's a hydrated electron. Just rip an electron off something and let it go in the water (not that it would survive there for long, but anyway). But dry electron sounds pretty weird to me. Dec 17 '15 at 15:14
• @Sosi - :-( again - A "dry electron" is a free electron which still has some of the kinetic energy from the event which created it. When it loses enough kinetic energy so that it becomes solvated then it is $e^{-}_{(aq)}$.
– MaxW
Dec 17 '15 at 15:17
• Yes, I got that; I just wanted to note that it still sounds strange to me. Dec 17 '15 at 15:18

A "dry" electron is an electron released from the event of an ionization. Depend on source the electron can either be defined as:

"The $e^-$ is a 'dry electron' that still retains some of the excess kinetic energy acquired from the ionizing event."$\ce{^{[1]}}$

or,

"The 'dry-electron' (defined as an electron before solvation) ..."$\ce{^{[2]}}$

A dry electron is thus, an electron that is not assiciated with any atoms, molecules or solutions.

Reference

$\ce{[1]}$ Thormod Henriksen, David H. Maillie; Radiation and Health; page 157

$\ce{[2]}$ J.D. Simon; Ultrafast Dynamics of Chemical Systems; page 144