Probing the vibrational and electronic structures of azide contact ion pairs in DMSO with fourier-transform infrared and soft x-ray absorption spectroscopy
9 affiliations
- 1Max Born Institute for Nonlinear Optics & Short Pulse Spectroscopy, Max Born Str. 2A, Berlin, Germany, 12489
- 2Department of Physics
- 3Stockholm University, AlbaNova University Center
- 4Institut für Chemie
- 5Martin-Luther-Universität Halle-Wittenberg
- 6Department of Physics and Astronomy
- 7Uppsala University
- 8Institute for Methods and Instrumentation for Synchrotron Radiation Research
- 9Helmholtz-Zentrum Berlin für Materialien und Energie GmbH
Abstract
The azide ion (N 3 - ) is a highly sensitive vibrational probe for investigating ion–pair interactions in solution. In dimethylsulfoxide (DMSO), N 3 - forms contact ion pairs with cations, leading to two distinct asymmetric stretching bands in the Fourier transform infrared (FT-IR) spectrum. Although this seems obvious, distinguishing different ion-pair species in detail becomes challenging because vibrational features overlap in the linear IR spectra. To obtain more insight into this apparent complexity, we employed two-dimensional correlation spectroscopy (2D-COS) in combination with molecular dynamics (MD) simulations to precisely distinguish the overlapping ion-pair species. Complementing the structural information from IR spectroscopy we used soft X-ray absorption spectroscopy (XAS) at the N K-edge to reveal the electronic interactions underlying the ion-pairing and to distinguish the effect of counter-ions on each atom of N 3 - separately. Combined with calculated spectra, our study demonstrates that nitrogen K-edge XAS, by probing transitions of nitrogen 1s core electrons to unoccupied molecular orbitals, directly reflects how the local electronic structure of N 3 - is affected by ion pairing. We provide evidence, in particular, for ion pairing results due to hybridization of unoccupied orbitals of N 3 - with valence orbitals of the adjacent Na + and Ca 2+ cations.
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BibTeX
@misc{rana2026probing,
title = {{Probing the vibrational and electronic structures of azide contact ion pairs in DMSO with fourier-transform infrared and soft x-ray absorption spectroscopy}},
author = {Debkumar Rana and Sambit K. Das and Anna Luisa Upterworth and Marc-Oliver Winghart and Mate Kurucz and Victoria Kabanova and Sebastian Eckert and Mattis Fondell and Philippe Wernet and Daniel Sebastiani and Michael Odelius and Erik T. J. Nibbering},
howpublished = {ChemRxiv},
year = {2026},
month = oct,
doi = {10.26434/chemrxiv.15010366/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010366/v1},
note = {CC BY-NC-ND},
}
RIS
TY - UNPB
TI - Probing the vibrational and electronic structures of azide contact ion pairs in DMSO with fourier-transform infrared and soft x-ray absorption spectroscopy
AU - Debkumar Rana
AU - Sambit K. Das
AU - Anna Luisa Upterworth
AU - Marc-Oliver Winghart
AU - Mate Kurucz
AU - Victoria Kabanova
AU - Sebastian Eckert
AU - Mattis Fondell
AU - Philippe Wernet
AU - Daniel Sebastiani
AU - Michael Odelius
AU - Erik T. J. Nibbering
PY - 2026
DA - 2026/10/13
PB - ChemRxiv
DO - 10.26434/chemrxiv.15010366/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010366/v1
AB - The azide ion (N 3 - ) is a highly sensitive vibrational probe for investigating ion–pair interactions in solution. In dimethylsulfoxide (DMSO), N 3 - forms contact ion pairs with cations, leading to two distinct asymmetric stretching bands in the Fourier transform infrared (FT-IR) spectrum. Although this seems obvious, distinguishing different ion-pair species in detail becomes challenging because vibrational features overlap in the linear IR spectra. To obtain more insight into this apparent complexity, we employed two-dimensional correlation spectroscopy (2D-COS) in combination with molecular dynamics (MD) simulations to precisely distinguish the overlapping ion-pair species. Complementing the structural information from IR spectroscopy we used soft X-ray absorption spectroscopy (XAS) at the N K-edge to reveal the electronic interactions underlying the ion-pairing and to distinguish the effect of counter-ions on each atom of N 3 - separately. Combined with calculated spectra, our study demonstrates that nitrogen K-edge XAS, by probing transitions of nitrogen 1s core electrons to unoccupied molecular orbitals, directly reflects how the local electronic structure of N 3 - is affected by ion pairing. We provide evidence, in particular, for ion pairing results due to hybridization of unoccupied orbitals of N 3 - with valence orbitals of the adjacent Na + and Ca 2+ cations.
ER -