## 4 Discussion
Hence, we have considered two possible situations to explain the generation of these unreachable charge states; one involves the charge transfer (CT) process shown in Figure 4, while the other is the occurrence of the higher-order ionization process. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Process** & **Channel** & \(\rm R_{ij}\) **(Å)** & \(\rm T_{ij\to n,m}\) **(fs)** \\ \hline \multirow{4}{*}{(a)} & (1, 1)\(\rightarrow\)(1, 2) & 3.80 & 17.55 \\  & (1, 2)\(\rightarrow\)(2, 2) & 4.84 & 16.25 \\  & (2, 2)\(\rightarrow\)(2, 3) & 4.86 & 7.28 \\  & (2, 3)\(\rightarrow\)(3, 3) & 5.49 & 9.13 \\  & (3, 3)\(\rightarrow\)(4, 3) & 5.35 & / \\ \hline \multirow{4}{*}{(b)} & (1, 1)\(\rightarrow\)(1, 2) & 3.80 & 17.55 \\  & (1, 2)\(\rightarrow\)(2, 2) & 4.84 & 16.25 \\  & (2, 2)\(\rightarrow\)(3, 2) & 5.33 & 11.73 \\  & (3, 2)\(\rightarrow\)(3, 3) & 5.14 & / \\ \hline \multirow{4}{*}{(c)} & (1, 1)\(\rightarrow\)(2, 1) & 4.22 & 20.55 \\  & (2, 1)\(\rightarrow\)(2, 2) & 4.55 & 9.86 \\  & (2, 2)\(\rightarrow\)(2, 3) & 4.86 & 7.28 \\  & (2, 3)\(\rightarrow\)(3, 3) & 5.49 & 9.13 \\  & (3, 3)\(\rightarrow\)(4, 3) & 5.35 & / \\ \hline \multirow{4}{*}{(d)} & (1, 1)\(\rightarrow\)(2, 1) & 4.22 & 20.55 \\  & (2, 1)\(\rightarrow\)(2, 2) & 4.55 & 9.86 \\  & (2, 2)\(\rightarrow\)(3, 2) & 5.33 & 11.73 \\  & (3, 2)\(\rightarrow\)(3, 3) & 5.14 & / \\ \hline \multirow{4}{*}{(e)} & (1, 1)\(\rightarrow\)(2, 1) & 4.22 & 20.55 \\  & (2, 1)\(\rightarrow\)(3, 1) & 4.16 & / \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The critical distance \(\rm R_{ij}\) and the travel time, \(\rm T_{ij\to n,m}\), for each channel of one-electron sequential ionization. First, we consider the effects of the existence of a CT process on the one-electron sequential ionization process. Here, the CT process is defined as \(\rm A^{+q}B^{+q}\)\(\rm A^{+q-1}B^{+q+1}\), as Ref. [48] mentioned. Here, the tunneling ionization process is not taken into account while performing the computation using the over-the-barrier (OBI) model. This makes sense because there is not much time for tunneling because the pulses are so short. The outer electrons are thought to move in the double-well potential U:  
\[\rm U=-\frac{Q_{1}/2}{|x+R/2|}-\frac{Q_{2}/2}{|x-R/2|}-\varepsilon x, \tag{10}\]  
where \(Q_{1}\) and \(Q_{2}\) represent the atomic core charges, \(x\) represents the axial position, R represents the internuclear separation, and \(\varepsilon\) is the laser E-field. The outer electron's energy level, \(E_{L}\), can be approximated by  
\[E_{L}=-\frac{(-E_{1}-Q_{2}/R)+(-E_{2}-Q_{1}/R)}{2}, \tag{11}\]  
where \(E_{1}\) and \(E_{2}\) are the known ionization potentials of the atomic ions. Figure 5 illustrates the procedure for calculating the charge transfer. The R is tiny in Figure 5a, and the center barrier is much lower than the \(E_{L}\) (the laser electric field introduces a considerable Stark shift, \(E=\epsilon\cdot R/2\)). As a result, CT may occur effortlessly. At the intermediate R shown in Figure 5b, both the central barrier and \(E_{L}\) increase. Because the central barrier increases faster than \(E_{L}\), the probability of CT decreases. When the probability of the charge transfer is zero, we can define the distance between the cores as \(R_{cr}\). In Figure 5c, the R is beyond \(R_{cr}\) and the \(E_{L}\) is already lower than the central barrier, so that the CT process does not occur. Within the experimental conditions, the \(R_{cr}\) of each CT channel can be calculated and is labeled in Table 3.  
Figure 4: Molecular IBr’s one-electron ionization pathways. The values situated above the arrow signify R (Å) during ionization. Charge transfer is represented by CT. Processes indicated by solid arrows are acceptable, whereas those indicated by dotted arrows are not. In Table 3, the first column represents the possible CT channels during the ionization process. The single arrow indicates the ionization process, and the double arrow represents the CT process. The second column represents the stretched value of the nuclear spacing when ionization occurs.