Spectroscopy of corannulene cations in helium nanodroplets

TL;DR

This study uses helium nanodroplet spectroscopy to analyze corannulene cations, revealing detailed absorption spectra, solvation structures, and differences between radical and protonated ions, advancing understanding of molecular ion spectroscopy.

Contribution

It introduces a novel helium tagging spectroscopy method for corannulene cations, identifying solvation structures and spectral differences with protonation, supported by atomistic modeling.

Findings

Identified 13 absorption bands of corannulene cations between 5500 Å and 6000 Å.

Observed small redshift in absorption bands due to helium solvation.

Protonated corannulene ions show broad absorption features unlike radical cations.

Abstract

Helium tagging in action spectroscopy is an efficient method for measuring the absorption spectrum of complex molecular ions with minimal perturbations to the gas phase spectrum. We have used superfluid helium nanodroplets doped with corannulene to prepare cations of these molecules complexed with different numbers of He atoms. In total we identify 13 different absorption bands from corannulene cations between 5500 {\AA} and 6000 {\AA}. The He atoms cause a small, chemically induced redshift to the band positions of the corannulene ion. By studying this effect as a function of the number of solvating atoms we are able to identify the formation of solvation structures that are not visible in the mass spectrum. The solvation features detected with the action spectroscopy agree very well with the results of atomistic modeling based on path-integral molecular dynamics simulations. By additionally doping our He droplets with D$_2$, we produce protonated corannulene ions. The absorption spectrum of these ions differs significantly from the case of the radical cations as the numerous narrow bands are replaced by a broad absorption feature that spans nearly 2000 {\AA} in width.