Oriented polar molecules trapped in cold helium nanodroplets: Electrostatic deflection, size separation, and charge migration

TL;DR

This paper demonstrates a method using electrostatic deflection to manipulate, size-separate, and study polar molecules in helium nanodroplets, enabling new insights into their properties and charge migration.

Contribution

It introduces a broadly applicable electrostatic deflection technique for polar molecules in helium nanodroplets, allowing size filtering and charge migration analysis.

Findings

Effective size separation of nanodroplets via deflection.

Measurement of dopant ionization probability as a function of droplet size.

Determination of charge hopping mean free path in helium matrix.

Abstract

Helium nanodroplets doped with polar molecules are studied by electrostatic deflection. This broadly applicable method allows even polyatomic molecules to attain sub-Kelvin temperatures and nearly full orientation in the field. The resulting intense force from the field gradient strongly deflects even droplets with tens of thousands of atoms, the most massive neutral systems studied by beam "deflectometry." We use the deflections to extract droplet size distributions. Moreover, since each host droplet deflects according to its mass, spatial filtering of the deflected beam translates into size filtering of neutral fragile nanodroplets. As an example, we measure the dopant ionization probability as a function of droplet radius and determine the mean free path for charge hopping through the helium matrix. The technique will enable separation of doped and neat nanodroplets and size-dependent spectroscopic studies.