The ambient-pressure endstation and branchline of the Versatile Soft X-ray (VerSoX) beamline B07 at Diamond Light Source serves a very diverse user community studying heterogeneous catalysts, pharmaceuticals and biomaterials under realistic conditions, liquids and ices, and novel electronic, photonic and battery materials. The instrument facilitates studies of the near-surface chemical composition, electronic and geometric structure of a variety of samples using X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine-structure (NEXAFS) spectroscopy in the photon energy range from 170 eV to 2800 eV. The beamline provides a resolving power hν/Δ(hν) > 5000 at a photon flux > 1010 photons s−1 over most of its energy range. By operating the optical elements in a low-pressure oxygen atmosphere, carbon contamination can be almost completely eliminated, which makes the beamline particularly suitable for carbon K-edge NEXAFS. The endstation can be operated at pressures up to 100 mbar, whereby XPS can be routinely performed up to 30 mbar. A selection of typical data demonstrates the capability of the instrument to analyse details of the surface composition of solid samples under ambient-pressure conditions using XPS and NEXAFS. In addition, it offers a convenient way of analysing the gas phase through X-ray absorption spectroscopy. Short XPS spectra can be measured at a time scale of tens of seconds. The shortest data acquisition times for NEXAFS are around 0.5 s per data point.

In situ photoemission and near-edge X-ray absorption fine structure (NEXAFS) techniques have been used to study the interaction of CO 2 with an ionic liquid thin film. A thin film of the superbasic ionic liquid (SBIL) trihexyltetradecylphosphonium benzimidazolide ([P 66614 ][benzim]) was prepared on a rutile TiO 2 (110) surface and exposed to CO 2 at near-ambient pressures. NEXAFS measurements combined with density functional theory calculations indicate a realignment of [benzim] − anions from 27°from the surface normal to 54°upon exposure to CO 2 . Angle-resolved X-ray photoelectron spectroscopy (AR-XPS) shows evidence of irreversible CO 2 absorption in thin films of [P 66614 ][benzim] and a greater concentration of CO 2 -reacted anions in the deeper layers. These results give a new perspective on CO 2 uptake in ionic liquids and fundamental interactions at the liquid−gas interface. Understanding this interfacial behavior is important for developing ILs for gas capture applications and may influence the performance of other IL-based technologies.

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