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Nick Besley Infrared Spectroscopy of a Small.pdf (1.64 MB)

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

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journal contribution
posted on 2020-07-31, 07:50 authored by 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.

History

Citation

J. Chem. Phys. 151, 194307 (2019); https://doi.org/10.1063/1.5124137

Author affiliation

Department of Chemistry

Version

  • AM (Accepted Manuscript)

Published in

Journal of Chemical Physics

Volume

151

Issue

19

Publisher

AIP Publishing

issn

0021-9606

eissn

1089-7690

Acceptance date

2019-10-01

Copyright date

2019

Spatial coverage

United States

Language

English

Publisher version

https://aip.scitation.org/doi/10.1063/1.5124137