[en] Convolution problems of time-resolved X-ray diffraction in liquids are studied theoretically. The model system under consideration is a diluted solution of diatomic molecules A_2 in a chemically inert solvent. This solution is submitted to a sub-picosecond laser pulse, which promotes molecule A_2 into an excited electronic state; the molecule then returns gradually into its ground state. The effects of finite duration of probing X-ray pulses on the X-ray signals are examined on this model. Variations of molecular geometry are clearly visible if the X-ray pulse duration is shorter than or comparable to molecular dynamics. They cease to be observable if they are much longer. Moreover, the effect of insufficient temporal location of the probing X-ray pulse with respect to that of the exciting laser pulse is examined. Dynamical effects are better seen in r-resolved, than in q-resolved signals. This theory is applied to the experimental study of recombination of laser excited I_2 in CCl_4. A careful deconvolution of experimental signals is necessary when synchrotron X-ray sources are applied. Proceeding in this way, motions of recombining I atoms are monitored from an initial distance of 5 A up to their final touch of 2.7 A. The birth of a new I_2 molecule can be visualized by this technique. (authors)