  Droplets provide unique opportunities for the investigation of laser-induced
surface chemistry. Chemical reactions on the surface of charged droplets are
ubiquitous in nature and can provide critical insight into more efficient
processes for industrial chemical production. Here, we demonstrate the
application of the reaction nanoscopy technique to strong-field ionized
nanodroplets of propanediol (PDO). The technique's sensitivity to the
near-field around the droplet allows for the in-situ characterization of the
average droplet size and charge. The use of ultrashort laser pulses enables
control of the amount of surface charge by the laser intensity. Moreover, we
demonstrate the surface chemical sensitivity of reaction nanoscopy by comparing
droplets of the isomers 1,2-PDO and 1,3-PDO in their ion emission and
fragmentation channels. Referencing the ion yields to gas-phase data, we find
an enhanced production of methyl cations from droplets of the 1,2-PDO isomer.
Density functional theory simulations support that this enhancement is due to
the alignment of 1,2-PDO molecules on the surface. The results pave the way
towards spatio-temporal observations of charge dynamics and surface reactions
on droplets in pump-probe studies.
