Probing interactions between core-electron transitions by ultrafast two-dimensional x-ray coherent correlation spectroscopy.

Two-dimensional x-ray correlation spectra (2DXCS) obtained by varying two delay periods in a time-resolved coherent all-x-ray four-wave-mixing measurement are simulated for the N 1s and O 1s transitions of aminophenol. The necessary valence and core-excited states are calculated using singly and doubly substituted Kohn-Sham determinants within the equivalent-core approximation. Sum-over-states calculations of the 2DXCS signals of aminophenol isomers illustrate how novel information about electronic states can be extracted from the 2D spectra. Specific signatures of valence and core-excited states are identified in the diagonal and off-diagonal peaks arising from core transitions of the same and different types, respectively.