Understanding proton transfer (PT) dynamics in condensed
phases
is crucial in chemistry. We computed a 2D map of N 1s X-ray photoelectron/absorption
spectroscopy (XPS/XAS) for an organic donor–acceptor salt crystal
against two varying N–H distances to track proton motions.
Our results provide a continuous spectroscopic mapping of O–H···N↔O–··· H+–N processes
via hydrogen bonds at both nitrogens, demonstrating the sensitivity
of N 1s transient XPS/XAS to hydrogen positions and PT. By reducing
the O–H length at N1 by only 0.2 Å, we achieved excellent
theory-experiment agreement in both XPS and XAS. Our study highlights
the challenge in refining proton positions in experimental crystal
structures by periodic geometry optimizations and proposes an alternative
scaled snapshot protocol as a more effective approach. This work provides
valuable insights into X-ray spectra for correlated PT dynamics in
complex crystals, benefiting future experimental studies.