A full multiple theor. model (MXAN) is applied to fit picosecond difference x-ray absorption spectra at the Ru L3 edge upon photoexcitation of aq. [RuII(bpy)3]2+. Fitting difference spectra allows an increase in sensitivity, such that slight structural changes can be retrieved, which are not detected in fitting full spectra. The Ru-N bond distances of the excited complex in the 3MLCT state are in good agreement with recently published values. The implementation of the present approach to L-edge spectra and its high sensitivity opens opportunities for its extension to a large class of expts. where difference x-ray absorption spectra are recorded. [on SciFinder (R)]