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Infrared spectroscopy of a small ion solvated by helium: OH stretching region of HeN-HOCO+

Davies, Julia A.; Besley, Nicholas A.; Yang, Shengfu; Ellis, Andrew M.


Julia A. Davies

Nicholas A. Besley

Shengfu Yang

Andrew M. Ellis


Messenger spectroscopy is a well-established method for recording infrared (IR) spectra of molecular ions. It relies upon the tagging of weakly bound atoms or molecules, known as the “messenger,” to the ion of interest. The ideal tag species is helium since it has the weakest possible interaction with any molecular ion and is consequently the least likely to alter the structure and function. However, the attachment of a helium tag is challenging because of the exceptionally cold conditions that are inherently required. In this work, electron ionization of doped liquid helium nanodroplets has been used to create cations tagged with a variable number (N) of helium atoms. Mass-selective ion detection has made it possible to record IR spectra as a function of N, thus revealing the effect on the structure and charge distribution within the ionic core as solvation becomes more extensive. We illustrate this capability for protonated carbon dioxide tagged with up to 14 helium atoms, HeN–HOCO+. The first atom preferentially binds to the proton and results in a substantial redshift of 44 cm−1 for the OH stretching vibration, while the stepwise attachment of additional atoms up to N = 7 causes small and progressive blueshifts, which are attributed to the gradual formation of a ring of helium around the carbon atom. The methodology described herein offers a new route to obtain IR spectra of He-tagged ions and provides an insight into ion-solvent interactions at the molecular level.

Journal Article Type Article
Publication Date Nov 21, 2019
Journal The Journal of Chemical Physics
Print ISSN 0021-9606
Electronic ISSN 1089-7690
Publisher AIP Publishing
Peer Reviewed Peer Reviewed
Volume 151
Issue 19
Article Number 194307
APA6 Citation Davies, J. A., Besley, N. A., Yang, S., & Ellis, A. M. (2019). Infrared spectroscopy of a small ion solvated by helium: OH stretching region of HeN-HOCO+. Journal of Chemical Physics, 151(19),
Keywords Physical and Theoretical Chemistry; General Physics and Astronomy
Publisher URL
Additional Information This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Infrared spectroscopy of a small ion solvated by helium: OH stretching region of HeN−HOCO+
Julia A. Davies, Nicholas A. Besley, Shengfu Yang, and Andrew M. Ellis. The Journal of Chemical Physics 151:19 and may be found at


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