Electron Diffraction of Pyrene Nanoclusters Embedded in Superfluid Helium Droplets

Abstract

We report electron diffraction of pyrene nanoclusters embedded in superfluid helium droplets. Using a least-squares fitting procedure, we have been able to separate the contribution of helium from those of the pyrene nanoclusters and determine the most likely structures for dimers and trimers. We confirm that pyrene dimers form a parallel double-layer structure with an interlayer distance of 3.5 Å and suggest that pyrene trimers form a sandwich structure but that the molecular planes are not completely parallel. The relative contributions of the dimers and trimers are ~6:1. This work is an extension of our effort of solving structures of biological molecules using serial single-molecule electron diffraction imaging. The success of electron diffraction from an all-lightatom sample embedded in helium droplets offers reassuring evidence of the feasibility of this approach.

Electron diffraction as a structure tool for charged and neutral nanoclusters formed in superfluid helium droplets

“…53,54 For ionization of cluster doped droplets, we use the fourth harmonic of a Nd:YAG laser at 266 nm (4.66 eV) without a focus lens. 55 At laser intensities of 10 6 W cm −2 or below, single- or 2-photon ionization of aromatic molecules (IE of pyrene: 7.4 eV) 56,57 is achievable, with minimal fragmentation and energy dissipation inside the cluster. The presence of the helium jacket effectively prevents fragmentation, resulting in only ionized parent and clusters of pyrene.…”

“…3 shows the arrival time profile of a pulsed superfluid helium droplet beam doped with pyrene detected on a mesh electrode wired to an operational amplifier with a large negative feedback resistor. 55 The time constant of the amplifier circuit is less than 1 μs, but the decay constant of the detector is 300 μs. The horizontal axis is the flight time of the ions across the flight path of 6 cm from the ionization region to the detector located near the diffraction region (Fig.…”

Experimental and theoretical study of photo-dissociation spectroscopy of pyrene dimer radical cations stored in a compact electrostatic ion storage ring

“…This model has been shown to cure the charge resonance issue(34). It has been used to determine the structural and energetic properties of pyrene cluster cations (33) and turned out to provide a fair agreement with experimental results addressing their thermal evaporation (35), ionization energies (36) and structural properties (37). The equilibrium structure of the (C16H10)2 + ion was found (33) not to be in an eclipsed superimposed parallel D2h arrangement but to present a twist (54 degrees) of the two units around the intermolecular axis, and also a significant dihedral angle between the two molecular planes, resulting in C1 symmetry.…”

Dynamical simulation of collision-induced dissociation of pyrene dimer cation

“…The investigation of PAH clusters has been performed from both the experimental and theoretical sides. From the experimental side, many studies focused on the investigation of structural properties of these clusters at the most stable geometrical configurations [5,7,[16][17][18][19]. Their energetic properties such as ionisation potentials have been recorded [20] as well as their spectral properties [21][22][23][24].…”