Structural Sensitivity of N 1s Excitations in <i>N</i>-Methylacetamide Solutions

Interpreting the X-ray spectra of liquids is complicated by their selective structural sensitivity and ensemble averaging. We report nitrogen K-edge spectra of liquid <i>N</i>-methylacetamide and its water solutions at temperatures of 305 and 350 K. The pre-peak in the spectrum shows a shift with an increase in the temperature or <i>N</i>-methylacetamide concentration. The effect is reproduced by our classical molecular dynamics simulations and subsequent spectrum calculations using density functional theory. We apply a data-driven method, emulator-based component analysis, to the computational data to identify the decisive structural degrees of freedom behind spectral variation. This representation in reduced dimensions accounts for the involved loss of structural information and reveals that the effect is indicative of weakening of the hydrogen bonds.