The solvation of electrons by an atmospheric-pressure plasma

TLDR

Solvated electrons are usually produced by radiolysis or photoionization, and although plasmas containing free electrons have been used with liquids for centuries, evidence of electron solvation by this approach has been scarce. This work reports direct measurements of solvated electrons generated by an atmospheric‑pressure plasma in contact with an aqueous surface. The electrons were detected via their optical absorbance in a total internal reflection geometry. The absorption spectrum is unexpectedly blue‑shifted, likely due to the intense electric field in the interfacial Debye layer; the electrons penetrate about 2.5 nm before recombining, and their reaction kinetics with scavengers are similar but not identical to those of bulk radiolysis‑generated solvated electrons.

Abstract

Solvated electrons are typically generated by radiolysis or photoionization of solutes. While plasmas containing free electrons have been brought into contact with liquids in studies dating back centuries, there has been little evidence that electrons are solvated by this approach. Here we report direct measurements of solvated electrons generated by an atmospheric-pressure plasma in contact with the surface of an aqueous solution. The electrons are measured by their optical absorbance using a total internal reflection geometry. The measured absorption spectrum is unexpectedly blue shifted, which is potentially due to the intense electric field in the interfacial Debye layer. We estimate an average penetration depth of 2.5 ± 1.0 nm, indicating that the electrons fully solvate before reacting through second-order recombination. Reactions with various electron scavengers including H(+), NO2(-), NO3(-) and H2O2 show that the kinetics are similar, but not identical, to those for solvated electrons formed in bulk water by radiolysis.