We report the electron diffraction of cationic pyrene (C16H10) clusters embedded in superfluid helium droplets. The diffraction profile contains a significant contribution from helium, but interferences of atomic pairs of pyrene are still recognizable. From least-squares fittings, we determine an interlayer distance of 3.0 Å for the cationic cluster, shortened from 3.5 Å in neutral clusters. The relative contributions of dimers and trimers are about 2:1, in qualitative agreement with the doping statistics. Limited by the detection range of the experimental data, we cannot distinguish further structure details. The predominant contribution of helium also prevents observations of the solvation shell of the ionic cluster. Nevertheless, the success of this experiment demonstrates the feasibility of electron diffraction from an ionic all-light-atom system, dispelling the concern over limited particle concentration of ionic species in the diffraction region, and the need of heavy atoms for diffraction intensity.

We report electron diffraction of cationic argon nanoclusters embedded in superfluid helium droplets. Superfluid helium droplets are first doped with neutral argon atoms to form nanoclusters, and then the doped droplets are ionized by electrons. The much lower ionization energy of argon ensures that the positive charge resides on the Ar nanocluster. Using different stagnation temperatures therefore droplets with different sizes, we have been able to preferentially form a small ionic cluster containing 2 -4 Ar atoms and a larger cluster containing 7 -11 atoms. The fitting results of the diffraction profiles agree with structures reported from theoretical calculations, containing a cationic trimer core with the remaining atoms largely neutral. This work testifies to the feasibility of performing electron diffraction from ionic species embedded in superfluid helium droplets, dispelling the concern over the particle density in the diffraction region. However, the large number of neutral helium atoms surrounding the cationic nanoclusters poses a challenge for the detection of the helium solvation layer, and the detection of which awaits further technological improvements.

We perform electron diffraction of 1,4-dichlorobenzene (C6H4Cl2, referred to as 2ClB) embedded in superfluid helium droplets to investigate the structure evolution of cluster growth. Multivariable linear regression fittings are used...