Direct detection of polar structure formation in helium nanodroplets by beam deflection measurements

TL;DR

This paper introduces a method using beam deflection measurements to directly detect and characterize polar structures within helium nanodroplets, revealing their electric dipole moments and aggregation behavior.

Contribution

It presents a novel electrostatic deflection technique to identify polar structures in helium nanodroplets and measure their dipole moments, complementing spectroscopic methods.

Findings

Successful detection of polar structures in helium nanodroplets.

Measurement of electric dipole moments of DMSO dimers and trimers.

Theoretical mapping of potential energy surfaces and aggregation dynamics.

Abstract

Long-range intermolecular forces are able to steer polar molecules submerged in superfluid helium nanodroplets into highly polar metastable configurations. We demonstrate that the presence of such special structures can be identified, in a direct and determinative way, by electrostatic deflection of the doped nanodroplet beam. The measurement also establishes the structures' electric dipole moments. In consequence, the introduced approach is complementary to spectroscopic studies of low-temperature molecular assembly reactions. It is enabled by the fact that within the cold superfluid matrix the molecular dipoles become nearly completely oriented by the applied electric field. As a result, the massive (tens of thousands of helium atoms) nanodroplets undergo significant deflections. The method is illustrated here by an application to dimers and trimers of dimethyl sulfoxide (DMSO) molecules. We interpret the experimental results with ab initio theory, mapping the potential energy surface of DMSO complexes and simulating their low temperature aggregation dynamics.