  Interactions between proteins and their solvent environment can be studied in
a bottom-up approach using hydrogen-bonded chromophore-solvent clusters. The
ultrafast dynamics following UV-light-induced electronic excitation of the
chromophores, potential radiation-damage, and their dependence on solvation are
important open questions. The microsolvation effect is challenging to study due
to the inherent mix of the produced gas-phase aggregates. We used the deflector
to spatially separate different molecular species in combination with
pump-probe velocity-map-imaging experiments. We demonstrated that this powerful
experimental approach reveals intimate details of the UV-induced dynamics in
the near-UV-absorbing prototypical biomolecular indole-water system. We
determined the time-dependent appearance of the different reaction products and
disentangled the occurring ultrafast processes. This novel approach ensures
that the reactants are well-known and that detailed characteristics of the
specific reaction products are accessible -- paving the way for the complete
chemical-reactivity experiment.
