Understanding X ray Photoelectron Spectra of Ionic Liquids Experiments and Simulations of 1 Butyl 3 methylimidazolium Thiocyanate

We demonstrate a combined experimental and computational approach to probe the electronic structure and atomic environment of an ionic liquid, based on core level binding energies. The 1 butyl 3 methylimidazolium thiocyanate [C4C1Im][SCN] ionic liquid was studied using ab initio molecular dynamics, and results were compared against previously published and new experimental X ray photoelectron spectroscopy XPS data. The long held assumption that initial state effects in XPS dominate the measured binding energies is proven correct, which validates the established premise that the ground state electronic structure of the ionic liquid can be inferred directly from XPS measurements. A regression model based upon site electrostatic potentials and intramolecular bond lengths is shown to account accurately for variations in core level binding energies within the ionic liquid, demonstrating the important effect of long range interactions on the core levels and throwing into question the validity of traditional single ion pair ionic liquid calculations for interpreting XPS dat

Resonant X ray photoelectron spectroscopy identification of atomic contributions to valence states

Valence electronic structure is crucial for understanding and predicting reactivity. Valence non resonant Xray photoelectron spectroscopy NRXPS provides a direct method for probing the overall valence electronic structure. However, it is often difficult to separate the varying contributions to NRXPS; for example, contributions of solutes in solvents or functional groups in complex molecules. In this work we show that valence resonant X ray photoelectron spectroscopy RXPS is a vital tool for obtaining atomic contributions to valence states. We combine RXPS with NRXPS and density functional theory calculations to demonstrate the validity of using RXPS to identify atomic contributions for a range of solutes both neutral and ionic and solvents both molecular solvents and ionic liquids . Furthermore, the one electron picture of RXPS holds for all of the closed shell molecules ions studied, although the situation for an open shell metal complex is more complicated. Factors needed to obtain a strong RXPS signal are investigated in order to predict the types of systems RXPS will work best for; a balance of element electronegativity and bonding type is found to be important. Additionally, the dependence of RXPS spectra on both varying solvation environment and varying local covalent bonding is probed. We find that RXPS is a promising fingerprint method for identifying species in solution, due to the spectral shape having a strong dependence on local covalency but a weak dependence on solvation environmen