  Tautomers are ubiquitous throughout chemistry, and typically considered
inseparable in solution. Yet (bio)chemical activity is highly tautomer
specific, with common examples being the amino and nucleic acids. While
tautomers exist in an equilibrium in solution, in the cold environment of a
molecular beam the barrier to tautomerization is typically much too high for
interconversion, and tautomers can be considered separate species. Here we
demonstrate the separation of tautomers and production of tautomerically-pure
gas-phase samples. We show this for the 2-pyridone / 2-hydroxypyridine system,
an important structural motif in both uracil and cytosine. Spatial separation
of the tautomers is achieved via electrostatic deflection in strong
inhomogeneous fields. We furthermore collect tautomer-resolved photoelectron
spectra using femtosecond multiphoton ionization. This paves the way for
studying the structure-function-dynamic relationship on the level of individual
tautomers, using approaches that typically lack the resolution to do so, such
as ultrafast dynamics experiments.
