## 2 Calculation Methods  
### Reaction Dynamics Simulation  
ReaxFF molecular dynamics (ReaxFF-MD) has been widely utilized to investigate the reaction mechanisms of environmentally friendly insulating gas pyrolysis [2; 18]. The ReaxFF reaction force field describes the breaking and formation of chemical bonds based on bond order and the positions of each atom. The system's energy in ReaxFF is defined as follows:  
\[ \begin{split} E_{\text{system}}=E_{\text{bond}}+E_{\text{over}}+E_ {\text{under}}+E_{\text{val}}+E_{\text{pen}}\\ +E_{\text{tors}}+E_{\text{coa}}+E_{\text{conf}}+E_{\text{vdWaals}}+E_ {\text{Coulomb}}\end{split}  \tag{1}\]  
where \(E_{\text{system}}\) represents the total energy of the system, \(E_{\text{bond}}\) denotes to the bond energy, and \(E_{\text{over}}\) and \(E_{\text{under}}\) are the energy correction terms for overcoordination and undercoordination, respectively. \(E_{\text{val}}\), \(E_{\text{pen}}\), and \(E_{\text{coa}}\) correspond to the bond angle energy term, penalty energy term, and three-body conjugation term, respectively. \(E_{\text{tors}}\) refers to the torsion energy, and \(E_{\text{conf}}\) denotes the four-body energy conjugation. \(E_{\text{vdWaals}}\) and \(E_{\text{Coulomb}}\) represent the non-bonding van der Waals and Coulomb interactions, respectively. The reaction dynamics simulation in this study involves force field parameters for O-F, C-F, F-N, and C-N bonds, and others. Therefore, the relevant parameters for F and N were fitted based on the existing ReaxFF force field, with the fitting methods described in references [19; 20]. The reaction kinetics simulations for insulating gases, such as C\({}_{5}\)F\({}_{10}\)O, CF\({}_{3}\)SO\({}_{2}\)F, and C\({}_{4}\)F\({}_{7}\)N, were performed using the fitted parameters. The simulation results were consistent with those reported in the previous literature [6; 14; 18] and with the simulated force fields in [21], confirming the validity of the force fields used in this study. Additionally, the simulation results for PMVE gas in this paper align with the findings from previous studies [9; 10], further validating the reliability of the selected fitting force field. To explore the decomposition mechanism of the PMVE/N\({}_{2}\) gas mixture, one-periodic cube models were established, as shown in Figure 1. Considering both computational efficiency and cost, the number of PMVE molecules was set to 100. Table 1 presents the key parameters and simulation conditions for different mixing ratios. These parameters are consistent with the actual conditions of the mixed gas at 25 \({}^{\circ}\)C and 0.1 MPa. The time scale for reaction kinetics simulations is significantly different from the actual reaction time, and appropriately increasing the temperature does not alter the original reaction pathway. To reduce the computational cost of kinetic calculations, the temperature was increased to enhance the reaction rate during the simulation process [22]. Figure 1: Snapshot of the initial configuration of the PMVE-N\({}_{2}\) system. (Light blue for F atom, red for O atom, gray for C atom, and dark blue for N atom). It is important to emphasize that under typical macroscopic experimental conditions, N\({}_{2}\) does not decompose at temperatures ranging from 1600 to 2600 K [23]. However, in ReaxFF-MD simulations, temperature primarily influences the reaction rate rather than altering the reaction pathways [24; 25; 26]. Therefore, the simulation temperature can be appropriately adjusted to balance computational efficiency, facilitate trajectory observation, and ensure simulation accuracy. The reaction kinetics simulation begins by minimizing the system energy over 5 ps at 5 K using the NVE ensemble, followed by system equilibration for 5 ps at 300 K using both the NVT and NPT ensembles. Reaction kinetics were then simulated at different temperatures and mixing ratios in the NVT ensemble, with a simulation step size of 0.1 fs and a total simulation time of 1000 ps.