X-Ray-Induced Fragmentation of Imidazolium-Based Ionic Liquids Studied by Soft X-Ray Absorption Spectroscopy

We investigated the x-ray absorption spectroscopy (XAS) fingerprint of EMImTFSI ionic liquid (IL) and its fragmentation products created by x-ray irradiation. To accomplish this, we used an open geometry where an IL droplet is directly exposed in the vacuum chamber, and an enclosed geometry where the IL is confined in a cell covered by an x-ray transparent membrane. In the open geometry, the XAS signature was stable and consistent with experimental and theoretical spectra reported in the literature. In contrast, when the IL is enclosed, its XAS evolved continuously under x-ray illumination due to accumulation of volatile fragmentation products inside the closed cell, while they evaporate in the open geometry. The changes in the XAS from the core levels of relevant elements (C, N, S, F) together with density functional theory (DFT) calculations, allowed us to identify the chemical nature of the fragment products and the chemical bonds most vulnerable to rupture under soft x-ray irradiation.