Unraveling the spectral signatures of solvent ordering in K-edge XANES of aqueous Na .

The aqueous solvation structure of the Na ⁺ ion is studied both by molecular dynamics (MD) simulations and K-edge X-ray absorption near edge spectroscopy (XANES). We present a systematic study contrasting the differences in the predicted XANES spectra, using molecular configurations generated from classical and quantum MD. Using a set of suitable order parameters, we elucidate how the spectroscopic features are influenced by the local solvation structure around the Na ⁺ ion. Our findings suggest that XANES is sensitive to fluctuations between the first and second solvation shells and can distinguish between classical and quantum interaction representations used to generate molecular ensembles.