Probing the vibrational and electronic structures of azide contact ion pairs in DMSO with fourier-transform infrared and soft x-ray absorption spectroscopy
Year: 2026
Type: preprint
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.
Source: ChemRxiv
Language: English
Subfield: Atomic and Molecular Physics, and Optics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Awards: GRK 2670: Amphiphilie Plus: Selbstorganisation weicher Materie durch multiple nichtkovalente Wechselwirkungen, G2255897640, Transforming strong bonds: Orbital-specific x-ay spectroscopy will tell us how to, Femtosekundenspektroskopie und quantenchemische Molekulardynamiksimulationen von photoinduzierten Protonentransferprozessen in wässriger Lösung, G3631573628, Seeing clear where others can’t – X-rays uncover the birth of C-H activation catalysts and how they function, Photochemical pathways for bond rearrangements and spin dynamics in azides, Soft x-ray spectroscopy for ultra-dilute in operando catalysts: Using machine learning for spectrometer developments, G5404377299, G7129216282, Study of carrier transport in MAterials by time-Resolved specTroscopy with ultrashort soft X-ray light, G796431723, NAISS
OpenAlex ID: W7221603831