The Structure of p-Aminobenzoic Acid in Water: Studies Combining UV-Vis, NEXAFS and RIXS Spectroscopies

NEXAFS-RIXS and home laboratory-based UV-Vis absorption spectroscopy are combined to examine the speciation and electronic structure of para- aminobenzoic acid (PABA) in aqueous solution as a function of pH. DFT and TD- DFT electronic structure calculations reproduce the experimental trends and provide a correlation between the experimental HOMO↔LUMO gap as well as the electronic transitions between molecular orbitals in the non-ionic, anionic and cationic forms of PABA.