## 3 Results
### Timeline for Generation of Highly Charged Atomic Iodine Ions
The very high charge state (>24+) peaks reached their maxima at \(\sim\)100 fs time delay, meanwhile the abundance of mid and low high charge states increases (see Figure 2). In Figure 2a, one clearly sees the rising  
Figure 1: Ion Time of flight (TOF) spectra of CH\({}_{3}\)I at a photon energy of 1619 eV and a pulse duration of 50 fs. Different curves (color coded) correspond to selected pump–probe delay times (see legend). The pulse energy is estimated to be \(\sim\)0.2 mJ, based on 1.3 mJ upstream value and a transportation loss of 85%. ‘no overlap’ is considered to represent the case at zero delay time (see text). (**a**) Spectral range: <11 amu; (**b**) Spectral range: >10 amu. the \(x\)-axis is plotted in log scale. peaks of I\({}^{19+}\), I\({}^{21+}\), and I\({}^{24+}\) above the shoulders of the dominant C\({}^{2+}\) peaks. Also, becoming clear are the peaks of I\({}^{22+}\) and I\({}^{23+}\) which appear as a split branch on top of the fast C\({}^{2+}\) peak. Charge states of carbon ions up to 3+ were observed. The highest charge state reached does not depend on the delay time. As seen in Figure 1, C\({}^{3+}\) was produced with a single pulse or at short delay time. However, the abundance of these carbon ions shows a delay-time dependence, increasing for longer delay time. The contributions of iodine ions under the carbon peaks are not large enough to explain the changes in the carbon peaks which are dominant. With a single pulse, the carbon ion signal at all charge states reaches around the maxima, similar to the values at long delay time. This could be an indication of charge transfer from the iodine to the methyl group that was thwarted by the ionization with the probe pulse [10]. To illustrate the overall picture of the evolution of the iodine charge states, we integrated the signal under the spectral peaks of various charge states at different pump-probe times, as shown in Figure 3. The integral signal with a single pulse was subtracted from the integrated signal at all other delay times, i.e., using the single pulse spectrum as a reference. Clearly seen in Figure 3 is: (1) high charge states were enhanced and low charge states were partially depleted by the second FEL pulse, shown as the trend from negative to positive ion yield difference for increasing charge states; (2) at short delay time, the depletion of low charge states were stronger compared to that at long delay, shown as the trend of decreasing absolute ion yield difference for increasing delay time within the block for each different charge state; (3) long delay time favors the production of very high charge states, consistent with the theme that these charge states were suppressed at 20 fs delay (negative values for I\({}^{25+}\) to I\({}^{28+}\)); (4) 50 fs delay, which is equal to the pulse duration, is an odd point at which the low and very high charges are dramatically enhanced, but not the intermediate charge states, compared to the case at adjacent delay times. Figure 2: Ion TOF spectra as a function of pump–probe delay time at a photon energy of 1619 eV and a pulse duration of 50 fs. The color represents the ion signal per laser shot (arb. unit) (see color bar). The “0” delay corresponds to the case of no overlap between the two X-ray beams (see text). The positons for various charge states of iodine atomic ions are marked and labeled at the top of the figure. (**a**) Spectral range: mass/charge < 11 amu; (**b**) Spectral range: mass/charge > 10 amu. The \(x\)-axes are plotted in log scale. As roughly seen in Figure 2a, there seems to be a phase shift between the spectrum with single pulse and those at delays larger than 50 fs for charge states I\({}^{25+}\) to I\({}^{28+}\). The spectra of the same charge state region are shown in Figure 4, where a decay base line of the spectrum at 20 fs delay was subtracted from all spectra and the spectrum at 20 fs delay was amplified for clarity of comparison.