## 3 Results  
### Timeline for Generation of Highly Charged Atomic Iodine Ions  
With a photon energy of 1619 eV, the dominant ionization at the first ionization step by a single FEL pulse is the photoionization of the M\({}_{1}\) shell electrons of the iodine atom which have a binding energy of \(\sim\)1072 eV. The subsequent cascade Auger decay and sequential decay will lead to high charge states of iodine. The second laser pulse, arriving at a particular delay time, will further ionize the molecular ions, likely dissociating after being generated by the first pulse. At short delay time, the ionization by the second pulse kicks in while the ionization by the first pulse is still ongoing. At longer delay, the second pulse will ionize established charge states during molecular dissociation. We observed high charge states up to 29+ for iodine and 3+ for carbon, as shown in Figure 1a (C\({}^{4+}\) ion peaks marked in Figure 1a cannot be confirmed in the current experiment, because the estimated KE is \(\sim\)230 eV, an increase from that for 3+ is much higher than expected or measured in previous work [11]). In the case of 'no overlap', we moved one of the two split mirrors to avoid spatial overlap of the two X-ray pulses to experimentally mimic the situation of single pulse with the same total pulse energy as two separate pulses. To ensure 'no overlap', we also set a long time delay of 150 fs. This single pulse condition will be presented in figures as the case of zero delay. The true time zero, the zero reference for all pump-probe delays, was set by mechanically making the two split mirrors co-plane [8]. With a single pulse ('no overlap'), the overall production of highly charged iodine ions is minimum even though the interaction region volume doubled, in comparison with the high charge state yield by two pulses. In contrast, the production of high charge states of carbon is at maximum in the single pulse scenario, which is similar to the production at long delay time in the two-pulse scenario. The spectral peaks for I\({}^{21+}\) to I\({}^{23+}\) overlap with those for C\({}^{2+}\). Their contribution, however, broadened the C\({}^{2+}\) peaks and even leads to a split structure on top of the fast C\({}^{2+}\) peak at the delay time of 150 fs (see Figure 1a). The I\({}^{29+}\) peak also overlaps with a carbon peak, but is obviously seen on top of the slow C\({}^{3+}\) peak. It is possible that charge states of iodine higher than 29+ were produced but buried under the C\({}^{3+}\) peak, as barely seen at the valley between the two C\({}^{3+}\) peaks (see Figure 1a). Similarly, the \(l^{21+}\) appears between the two C\({}^{2+}\) peaks. The abundance of high charge states decreases for higher charges. The seemingly higher yield of I\({}^{16+}\) compared to the adjacent peaks is due to the contribution of O\({}^{2+}\) from the background gas in the vacuum chamber. The production of low charge states (I\({}^{+}\) to I\({}^{6+}\)) is favored at long delay time, reaching a maximum with a single pulse as shown in Figure 1b. At the low charge states, the ion yields at short (20 fs) and intermediate (\(\sim\)40 fs) delay times are similar. Figure 2 shows the TOF spectra as a function of pump-probe delay with a finer step size (see figure \(y\)-axis tick labels). The time zero spectrum corresponds to that with single pulse mentioned above. As seen in Figure 2, there is an overall drop in the ionization yield at short pump-probe delay time (20 fs). Particularly, the very high charge states (>24+) are almost vanished. Most CH\({}_{3}\)I molecular ions went through dissociation, since only a small amount of CH\({}_{3}\)I\({}^{+}\) remains (see Figure 1b). The first significant peak is I\({}^{+}\), which is much smaller compared to the dominant I\({}^{2+}\) peak, because Auger decay preferentially generates evenly charged ions and the charges are mainly localized. As the pump-probe delay time increases, the ion yield for high charge states increases within the pulse duration.