Abstract
Helium tagging in action spectroscopy is an efficient method for measuring the absorption spectra of complex molecular ions with minimal perturbations to the gas phase spectra. 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 Å and 6000 Å. The He atoms cause a small, chemically induced redshift of 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 using 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 D2, 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 Å in width.
Highlights
Messenger spectroscopy[1] with helium atoms as tags has in recent years paved the way for determining the previously unobtainable gas phase absorption spectra of complex molecules with the accuracies required for identifying the origin of astronomical absorption features
In total we identify 13 different absorption bands from corannulene cations between 5500 Aand 6000 A
This was demonstrated well in 2015 when C60+ was shown[2,3,4] to be the rst identi ed carrier of at least ve of the several hundred Diffuse Interstellar Bands (DIBs), the origin of which have been a mystery for nearly a century.[5]
Summary
Messenger spectroscopy[1] with helium atoms as tags has in recent years paved the way for determining the previously unobtainable gas phase absorption spectra of complex molecules with the accuracies required for identifying the origin of astronomical absorption features. This was demonstrated well in 2015 when C60+ was shown[2,3,4] to be the rst identi ed carrier of at least ve of the several hundred Diffuse Interstellar Bands (DIBs), the origin of which have been a mystery for nearly a century.[5] Maier and coworkers achieved this result by. By measuring the depletion of HenC60+ using a mass spectrometer as a function of wavelength and cluster size, the gas phase spectrum of bare fullerene ions could be deduced through interpolation down to n 1⁄4 0.2,6–8 The key bene t of using helium for spectroscopy in this way is the extremely weak interaction between the He atoms and the molecule being studied that gives a relatively small shi compared to other methods such as matrix isolation in solid neon and argon.[9,10]
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