## 3 Results and Discussion
### Dissociative Ionization of CHBrCl\({}_{2}\) Molecules in 800 nm Femtosecond Laser Fields  
The laser pulse duration in our experiment was 70 fs (FWHM), and it is reasonable that most single ionizations will take place in the first few cycles, then the dissociations will occur. Hence, the lower-velocity components of Cl\({}^{+}\), Br\({}^{+}\), CHBrCl\({}^{+}\), and CHCl\({}_{2}\)\({}^{+}\) ions should belong to the dissociative ionization of the single-charged molecular ion CHBrCl\({}_{2}\)\({}^{+}\). The estimated reaction pathways are listed as follows. Channel (1) CHBrCl\({}_{2}\)\(\rightarrow\) CHBrCl\({}_{2}\)\({}^{+}\) + e\({}^{-}\)\(\rightarrow\) Cl\({}^{+}\) + CHBrCl + e\({}^{-}\)  
Channel (2) CHBrCl\({}_{2}\)\(\rightarrow\) CHBrCl\({}_{2}\)\({}^{+}\) + e\({}^{-}\)\(\rightarrow\) Br\({}^{+}\) + CHCl\({}_{2}\) + e\({}^{-}\)  
To confirm these dissociation processes, the appearance energies (E\({}_{\text{AP(1)}}\) = 17.57 and E\({}_{\text{AP(2)}}\) = 15.65 eV) of the abovementioned channels were calculated, respectively. Appearance energies expressed in Equation (1) represent the required energy to switch on the channel, where E\({}_{\text{i}}\) and E\({}_{\text{j}}\) are the total energy of reaction products and reactants, respectively. \[\text{E}_{\text{AP}}=\Sigma\text{E}_{\text{i}}-\Sigma\text{E}_{\text{j}}, \tag{1}\]  
\[\text{E}_{\text{AV}}=\text{nhv}-\text{E}_{\text{AP}}, \tag{2}\]  
\[\text{E}_{\text{T}}=(\text{m}_{\text{a}}\text{V}_{\text{a}}{}^{2}/2)(\text{m}_{ \text{a}}+\text{m}_{\text{b}})/\text{m}_{\text{b}}, \tag{3}\]  
After absorbing enough photons and overcoming the ionization potential barrier, the redundant energy, which is named available energy (E\({}_{\text{AV}}\)) expressed in Equation (2), released into the internal energy of fragments, and the translational energy (E\({}_{\text{T}}\)) of the reaction channel. E\({}_{\text{T}}\) can be obtained by Equation (3), where V\({}_{\text{a}}\) denotes the velocity of fragment ions, and m\({}_{\text{a}}\) and m\({}_{\text{b}}\) represent the mass of fragment ion a and neutral fragment b, respectively. As listed in Table 1, the experimental results are in good agreement with the calculated results, which demonstrates that the above-estimated channels originate from the dissociative ionization of single-charged molecular ion CHBrCl\({}_{2}\)\({}^{+}\). Angular distribution of fragment ions also reflects the molecular dynamics process in an intense field. By integrating the reconstructed 2D velocity over a proper range of speed at each angle, the angular distributions of Cl\({}^{+}\) and Br\({}^{+}\) ions are shown in Figure 4. It was found that the angular distribution of Br\({}^{+}\) ion is isotropic, but that of Cl\({}^{+}\) ion is an anisotropic distribution parallel to the laser polarization direction. To explore the reasons for the above differences, we calculated the potential energy curves (PECs) of the excited states of the parent ion CHBrCl\({}_{2}\)\({}^{+}\) along the C-Cl and C-Br bonds. As shown in Figure 5, the equilibrium nuclear distance (R\({}_{\text{e}}\)) of the C-Cl and C-Br bonds of molecule CHBrCl\({}_{2}\) was 1.78 and 1.95 A, respectively. Following the Franck-Condon principle, the electron wave-packets of molecular ions CHBrCl\({}_{2}\)\({}^{+}\) was excited to the high-lying states at this equilibrium nuclear distance. Then, the electron wave-packets will evolve along the potential energy curve of the excited states Here, the minimum energy of the ground state was set to zero for the sake of convenience. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Channel** & **E\({}_{\text{AP}}\) (eV)** & **KERs (eV)** & **E\({}_{\text{T}}\) (eV)** & **E\({}_{\text{AV}}\) (eV)** \\ \hline (1) & 17.57 & 0.25 & 0.32 & 1.03 \\ (2) & 15.65 & 0.18 & 0.35 & 1.40 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The related results of the above-estimated reaction channels.