# Do bare protons exist, even transiently, in aqueous solution?

Generally $\ce{H^+}$ ions in water remain in the form of hydronium ions ($\ce{H3O+}$), and not as "free" aqueous protons, as far as I've been taught.

My question: is this always the case, even when considering dynamics at extremely short time scales? By this I am not meaning interconversion with the Zundel ($\ce{H5O2+}$) or other states. I mean to say, does bare $\ce{H+}(\mathrm{aq})$ ever exist on, say, a femtosecond time scale?

• I think this is one of those things where there probably is a single proton floating around somewhere in a solution, but the formation of this is so unlikely. It means that you need to have just a hydrogen atom somewhere in solution and some other molecule which will take that electron and form a radical, which is certainly not stabilizing. Then, the proton needs to somehow not react with anything for a femtosecond. My bet is that this just doesn't happen... – jheindel Feb 25 '16 at 2:26
• This is probably more of a philosophical question - when is a H bonded to something, and when is it not? That's quite tricky to answer, particularly in the liquid state... – Gerhard Feb 25 '16 at 13:24
• – getafix Jan 1 '18 at 19:19

But to put this into perspective, an electron-free proton has an estimated acidity $10^{56}$(!) times greater than 100% H2SO4, the threshold of superacidity.$^2$ Adding a bare proton to a molecule is a real event in the gas phase but only a solvated hydrogen ion can be transferred in condensed phases.