X-ray four-wave mixing signals generated in the ${\mathbf{k}}_1+{\mathbf{k}}_2-{\mathbf{k}}_3$ phase-matching direction are simulated for N $1s$ transitions in paranitroaniline and two-ring hydrocarbons disubstituted with an amine and a nitroso groups. The two-dimensional x-ray correlation spectra (2DXCS) provide background-free probes of couplings between core-electron transitions even for multiple core shells of the same type. Features attributed to couplings between spatially separated core transitions connected by delocalized valence excitations provide information about molecular geometry and electronic structure unavailable from linear near-edge x-ray absorption (XANES).

• Received 31 July 2008

DOI:https://doi.org/10.1103/PhysRevA.78.052509