Valence excitation of NO2 by impulsive stimulated x-ray Raman scattering

Impulsive x-ray Raman excitations are the components of multidimensional x-ray spectroscopies that have been proposed. However the question of the optimum laser parameters to use for these impulsive excitations is still open. The multiconfiguration time-dependent Hartree-Fock (MCTDHF) method includes a description of the wave function that makes no assumptions about the degree of excitation, correlation, or ionization of the wave function. Impulsive x-ray Raman valence excitations of the NO2 molecule driven by 1fs pulses tuned below the Oxygen K-edge were calculated in the fixed-nuclei approximation using the MCTDHF method. Fixing the duration but varying the central frequency and intensity of the pulse, not considering chirp, maximum population transfer is obtained at an intensity of approximately 3×10 W cm, with the central frequency substantially 8eV reddetuned from the 2nd order optimum, and most likely driven by nonresonant Raman with the Oxygen K-edge continuum. Strong nonlinear effects are present at 10 W cm. The results will hopefully help guide the selection of experimental conditions under which multidimensional X-ray spectroscopies are most viable.