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

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.

Strong permanent magnet gradient deflector for Stern–Gerlach-type experiments on molecular beams

“…Helpfully, in this case a reference undeflected profile can be acquired from an undoped, nonmagnetic, droplet beam without needing to switch off the field. This is analogous to recent electric deflection experiments on nanodroplets with embedded polar molecules 12,13 in which undoped nanodroplets were unaffected by passage between high-voltage deflection electrodes.…”

Oriented Polar Molecules Trapped in Cold Helium Nanodropets: Electrostatic Deflection, Size Separation, and Charge Migration

“…The same approach can be employed with interesting and unusual agglomerates produced via sequential pick-up (this also is a unique capability of helium nanodroplet embedding). For example, it can detect the formation of novel metastable assemblies of cold polar molecules, as we have demonstrated for DMSO dimers and trimers [57]. It should also be usable for the identification of polar vs. nonpolar conformers (cf.…”

Probing the presence and absence of metal-fullerene electron transfer reactions in helium nanodroplets by deflection measurements

“…For the conditions employed in the present measurements, the mean size was found to be ≈2×10 4 helium atoms per droplet. Using this information and the "field-off" profile as input, we perform a Monte Carlo simulation of the deflection, as detailed in our previous publications, 12,23,27,28 accounting for droplet shrinkage by evaporation and for the pick-up and ionization probabilities, and solve for the dipole moment of the embedded complex by fitting the simulated "field-on" profile to the data.…”