Figure 16
(a), (b) Pump–probe XES signal of 15 mM solution of Fe(bpy)32+ in acetonitrile while scanning the vertical position of the last mirror in the optical laser beam path (color coded in the upper picture). The maximum of the transient signal marks optimal spatial overlap of the laser and the X-ray beams. (c), (d) Then, the phase shifter of the optical laser is scanned to accurately determine time-zero (Fig. 18, right). The phase shifter value is color coded in the upper picture. Images were recorded with a CCD (from GreatEyes Co.) with 10 Hz frame rate. Exposure time was set to 5 s for every data point in (c) and (d), scans were done twice, once with exposure of the sample by the pump laser, and once without. The transient signals were obtained as the difference in sums of all background-corrected laser-on- and laser-off spectra recorded with the von Hamos spectrometer. |