Dataset pertaining to the article "Liquid-Jet Photoemission Spectroscopy as a Structural Tool: Site-Specific Acid-Base Chemistry of Vitamin C", submitted to Physical Chemistry Chemical Physics. Here, we demonstrate how liquid-jet photoemission spectroscopy can be systematically used for chemical analysis, probing tautomeric forms and deprotonation sites in aqueous vitamin C. We also present a fast and reliable computational protocol to model the spectra. Files with extension .h5 are hdf5-files structured according to the NeXus standard v2022.07, seehttps://www.nexusformat.org/https://fairmat-experimental.github.io/nexus-fairmat-proposal/50433d9039b3f33299bab338998acb5335cd8951/mpes-structure.htmlNeXus data files can be opened with any software capable of opening hdf5-structured files. The following viewers are adapted to the specifics of the NeXus data format:* nexpy (distributed with python)* https://h5web.panosc.eu/h5wasm (web-based NeXus viewer maintained by the European Photon and Neutron Open Science Cloud-consortium) The following files are provided: Photoemission data pertaining to vitamin C PES measurements: vitamin-C.h5 Computational data for Figures 3, 5, and 6: binding energy values (plain text) from which the spectra were modeled, optimized molecular geometries (XYZ coordinates, distances in angstroms) used in the calculations, and a sample input for the binding energy calculation. All data for each figure are packed in a zip file. COMPUTATIONAL-DATA-Fig3.zipCOMPUTATIONAL-DATA-Fig5.zipCOMPUTATIONAL-DATA-Fig6.zip Numeric representations of the traces shown in the article's figures (space-separated or comma-separated ascii-files): Figure 3:EXPT.datTAUTOMER-A.datTAUTOMER-B.datC2.datC3.datC5.datC6.datC2+C3.datC2+C5.datC2+C6.datC3+C5.datC3+C6.datC5+C6.dat Figure 5:EXPT.datTAUTOMER-A.datC3.datC2+C3.dat Figure 6:EXPT.datC3.datC3-UFF-ensemble.datC3-Bondi-single.datC3-Bondi-ensemble.datTAUTOMER-A.datTAUTOMER-A-ensemble.datC2+C3.datC2+C3-ensemble.dat Figure S1:EXPT.datEXPT-850eV.dat Version history:4: Data from version 2 reuploaded3: Experimental NeXus-data added2: Computational data and figure traces added1: Initial upload Contact person for questions regarding this data set: Lukas Tomanik, tomanikl@vscht.cz . If you use these data for your scientific work we are curious to learn about it.

Funding acknowledgements: L.T. and P.S. appreciate the support of the Czech Science Foundation (EXPRO project no. 21-26601X). L.T. was supported in the later stage of the project by the outgoing grant of the Czech Science Foundation, grant number 24-12267O. M.P. and B.W. acknowledge funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 883759, AQUACHIRAL). B.W. also acknowledges support from the MaxWater initiative of the Max-Planck-Gesellschaft. S.T. acknowledges support from the JSPS KAKENHI Grant No. JP20K15229. This work was supported by the project "The Energy Conversion and Storage", funded as project No. CZ.02.01.01/00/22_008/0004617 by Programme Johannes Amos Comenius, call Excellent Research.