Calculation of near-edge x-ray-absorption fine structure at finite temperatures: Spectral signatures of hydrogen bond breaking in liquid water

The near-edge x-ray-absorption fine structure of H₂O in the gas, hexagonal ice, and liquid phases were calculated using heuristic density functional based methods. It was demonstrated that the differences between the ice and water spectra could be rationalized in terms of the breaking of hydrogen bonds around the absorbing molecules. It was also demonstrated that the increase in pre-absorption feature from ice to water was due to the breaking of a donor hydrogen bond. It was found that approximately 19% of the hydrogen bonds were broken in the case of water.