Laser-induced Coulomb explosion imaging of \ce{(C6H5Br)2} and \ce{C6H5Br-I2} dimers in helium nanodroplets using the Timepix3

TL;DR

This study used laser-induced Coulomb explosion imaging with advanced 3D ion detection to determine the structures of bromobenzene-I2 and bromobenzene homodimers inside helium droplets, demonstrating a method for real-time molecular structure analysis.

Contribution

The paper introduces a novel application of Coulomb explosion imaging combined with Timepix3 detectors to determine the structures of large molecular complexes inside helium droplets.

Findings

Heterodimer has I2 axis perpendicular to phenyl ring.

Homodimer exhibits a stacked parallel structure.

Method enables real-time structural analysis of large complexes.

Abstract

We have deduced the structure of the \ce{bromobenzene}--\ce{I2} heterodimer and the \ce{(bromobenzene)2} homodimer inside helium droplets using a combination of laser-induced alignment, Coulomb explosion imaging, and three-dimensional ion imaging. The complexes were fixed in a variety of orientations in the laboratory frame, then in each case multiply ionized by an intense laser pulse. A three dimensional ion imaging detector, including a Timepix3 detector allowed us to measure the correlations between velocity vectors of different fragments and, in conjunction with classical simulations, work backward to the initial structure of the complex prior to explosion. For the heterodimer, we find that the \ce{I2} molecular axis intersects the phenyl ring of the bromobenzene approximately perpendicularly. The homodimer has a stacked parallel structure, with the two bromine atoms pointing in opposite directions. These results illustrate the ability of Coulomb explosion imaging to determine the structure of large complexes, and point the way toward real-time measurements of bimolecular reactions inside helium droplets.