## 3 Results and Discussion
### The Dissociative Ionization of Molecule \(\rm{CF_{2}Br_{2}}\) in 800 nm Laser Fields
The details of the structural changes are listed in Table 3. As shown in Table 3, the bond length for C-Br bonds is 1.96 A for the molecule CF\({}_{2}\)Br\({}_{2}\), and the distance of the two Br atoms is 3.24 A. After losing one electron, the C-Br bond length hardly changes, but the distance of two Br atoms shortens to 2.86 A and the bond angle of \(\angle\)Br-C-Br decreases from 112\({}^{\circ}\) to 92\({}^{\circ}\). The possible reason for this structure deformation is that the ionized electrons are mainly from non-bonding Highest Occupied Molecular Orbital(HOMO), where the electron cloud mostly distributes on the two bromine atoms. Then the ground state of singly charged molecular ions CF\({}_{2}\)Br\({}_{2}\)\({}^{+}\) becomes starting point for the elimination reaction. Both C-Br bonds length firstly increases from the 1.99 A to the 2.57 A. However, the distance of Br-Br decreases from 2.86 A to 2.30 A and the angle of \(\angle\)Br-C-Br decreases intensively from 92.0\({}^{\circ}\)to 53.2\({}^{\circ}\). Next, the TS\({}_{1}\) releases an energy of 0.09 eV to the transition state TS\({}_{2}\). In this process, the structural changes are very gentle, and two C-Br bond lengths slowly increase to 2.62 A. The distance of Br-Br and the bond angle \(\angle\)Br-C-Br remain almost unchanged. Finally, the TS\({}_{2}\) spontaneously evolves to the intermediate state IS. The C-Br(4) bond length shortens to 2.28 A, while the other C-Br(5) bond elongates to 3.45 A and the bond angle \(\angle\)Br-C-Br drops from 53.5\({}^{\circ}\) to 41.9\({}^{\circ}\). For the intermediate state IS, the distance of Br-Br equals the equilibrium internuclear distance of molecule Br\({}_{2}\). After the C-Br(5) bond cleavage, the molecular Br\({}_{2}\) and ion Br\({}_{2}\)\({}^{+}\) are produced from the channels four and five, respectively. However, the molecular Br\({}_{2}\) is not observed in our experiment because of the impossibility to detect neutral particles by a VMI setup. Therefore, the channel  
Figure 5: Natural bond orbital (NBO) charge distribution of CF\({}_{2}\)Br\({}_{2}\)\({}^{+}\) ions and the charge assignment of the corresponding dissociation channel. four is confirmed by the appearance of the fragment ion CF\({}_{2}\)\({}^{+}\) in the 400 nm laser field. **Channel** **Reaction Path**  
(4) \(\mathrm{CF_{2}Br_{2}^{+}\to CF_{2}^{+}+Br_{2}}\),  
(5) \(\mathrm{CF_{2}Br_{2}^{+}\to Br_{2}^{+}+CF_{2}}\),  
In addition, we argue that the hump for ions CF\({}_{2}\)\({}^{+}\) (0.76 eV) originate from the multiphoton dissociative process as channel three in the 400 nm laser field (\(\mathrm{E_{T}=1.00}\) eV, \(\mathrm{E_{AV}=2.99}\) eV @400 nm). For ions CF\({}_{2}\)Br\({}^{+}\)(0.75 eV) in the 400 nm laser field, it indicates a new reaction pathway different from channel reaction in the 800 nm case (See Figure 2c). Once passing through the transition state (\(\mathrm{E_{AP}=12.45}\) eV), the ions CF\({}_{2}\)Br\({}^{+}\) can be produced due to the Br-Br bond cleavage. The \(\mathrm{E_{K}}\) of ions CF\({}_{2}\)Br\({}^{+}\) in the 400 nm laser field is in accordance with the fact that the calculated values of channel six (\(\mathrm{E_{T}=1.97}\) eV, \(\mathrm{E_{AV}=3.05}\) eV @400 nm). Because of the much higher excitation efficiency to the transition state, channels four to six are the unique channels in the 400 nm laser field, which suggests that dissociative ionization processes are sensitive to laser wavelengths [28]. **Channel** **Reaction Path**  
(6) \(\mathrm{CF_{2}Br_{2}^{+}\to CF_{2}Br^{+}+Br}\)