  Solvent interactions, particularly hydration, are vital in chemical and
biochemical systems. Model systems unveil microscopic details of such
interactions. We uncover a specific hydrogen-bonding motif of the biomolecular
building block indole (C$_8$H$_7$N), tryptophan's chromophore, in water: a
strong localized $\text{N-H}\cdots\text{OH}_2$ hydrogen bond, alongside
unstructured solvent interactions. This insight is revealed from a combined
experimental and theoretical analysis of indole's electronic structure in
aqueous solution. We have recorded the complete X-ray photoemission and Auger
spectrum of aqueous-phase indole, quantitatively explaining all peaks through
\emph{ab initio} modeling. The efficient and accurate technique for modeling
valence and core photoemission spectra involves the maximum-overlap method and
the non-equilibrium polarizable-continuum model. A two-hole electron-population
analysis quantitatively describes the Auger spectra. Core-electron binding
energies for nitrogen and carbon highlight the specific interaction with a
hydrogen-bonded water molecule at the N-H group and otherwise nonspecific
solvent interactions.
