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.

Abstract

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.

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), Article 194307. https://doi.org/10.1063/1.5124137

• Journal Article Type: Article
• Acceptance Date: Oct 31, 2019
• Online Publication Date: Nov 20, 2019
• Publication Date: Nov 21, 2019
• Deposit Date: Nov 21, 2019
• Publicly Available Date: Nov 25, 2019
• Journal: The Journal of Chemical Physics
• Print ISSN: 0021-9606
• Electronic ISSN: 1089-7690
• Publisher: American Institute of Physics
• Peer Reviewed: Peer Reviewed
• Volume: 151
• Issue: 19
• Article Number: 194307
• DOI: https://doi.org/10.1063/1.5124137
• Keywords: Physical and Theoretical Chemistry; General Physics and Astronomy
• Public URL: https://nottingham-repository.worktribe.com/output/3350185
• Publisher URL: https://aip.scitation.org/doi/10.1063/1.5124137
• 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 https://aip.scitation.org/doi/10.1063/1.5124137