In situ detection of solvated oxygen atoms

As a diradical and powerful oxidant, atomic oxygen plays an integral role in a wide range of low temperature plasma applications. However, it remains difficult to account for, especially in the aqueous phase. Current detection techniques require inherently problematic chemical probes, which, along with a lack of chemical reference data, preclude a full understanding of its effects. Here we present a novel technique to detect solvated O atoms directly by employing femtosecond two-photon absorption laser induced fluorescence (TALIF). The use of an ultrafast laser provides sufficient excitation, without heating the liquid, to allow for the detection of laser-excited O despite the aggressive quenching environment in water. Critically, an effort is made to absolutely calibrate the recorded signal for density with molecular dynamics simulations of solvated O atoms. From this, currently unknown quantities for solvated O atoms can be estimated and a value for the previously unreported Henry’s law constant is given. Uncertainties are examined and the possible extension of this method to other atomic species of interest discussed. These measurements serve as a proof of concept for a powerful experimental technique to quantify solvated O densities directly without chemical probes.