Removing gas-phase features in near ambient pressure partial Auger-Meitner electron yield oxygen K-edge NEXAFS spectra

With the advent of ambient pressure X-ray excited electron spectroscopy, near-edge X-ray absorption fine structure spectroscopy is widely used to investigate the hydrogen-bonding environment in aqueous solutions, ice, and adsorbed water. When Auger-Meitner electrons are detected, the method becomes inherently surface-sensitive because of the limited escape depth of electrons. In such X-ray absorption experiments with aqueous samples, gas-phase water is inevitably present. It impacts the acquired spectra in two ways: (1) Absorption along the X-ray path upstream of the sample reduces the photon flux reaching the condensed phase. (2) Spectra originating from gas-phase water in front of the analyzer contribute to the recorded spectra. Here, we develop and discuss a procedure to disentangle the gas-phase and condensed-phase contribution in the acquired spectra. A novel approach to quantify and remove the gas-phase contribution allows receiving condensed-phase near-edge X-ray absorption fine structure spectra at high water vapor pressure free of gas-phase artifacts.