X-ray four-wave mixing in molecules

An effective core-exciton Hamiltonian is constructed for nitroanilines which includes 1s core hole transitions of both nitrogen atoms. The wavevector and frequency dependent third order susceptibility chi((3)) is calculated and used to predict the frequency-domain pump-probe spectra which show both photobleaching and excited state absorption components. Signatures of electron delocalization and differences among the para-, meta-, and ortho-isomers are discussed. (C) 2002 American Institute of Physics.