Probing Charge Transfer to Cold Molecules Within Superfluid Helium Nanodroplets

Helium nanodroplet isolation is a powerful and broadly applicable tool for the investigation and manipulation of cold molecules. One source of uncertainty in the mass spectrometry of droplet-embedded molecules is their ionization probability, i.e., the process of charge transfer from the helium matrix to the dopant molecule. We investigate this process by means of our recently developed deflection technique, whereby a beam of superfluid He nanodroplets doped with polar molecules is deflected by an external inhomogeneous electric field. The almost complete orientation of the cold embedded molecules results in a remarkably large beam deviation. Among the various applications of this technique is its ability to spread the deflected neutral beam according to the droplet size. Using this tool, we parameterize the intra-droplet charge transfer probability as a function of droplet size. The results are compared with theoretical models of charge hopping within the liquid helium medium.