## 3 Results and Discussion
### NH\({}_{3}\) Generation Mechanism  
In order to further investigate the reaction mechanism of ammonia synthesis by pulsed discharge plasma after the addition of noble gases, we analyzed the main reactions after the addition of Ar using a 0D ZDPlaskin reaction kinetics model. In this model, we used the optimal reaction conditions, i.e., the gas ratio of N\({}_{2}\):H\({}_{2}\) = 1, the addition of Ar of 40%, the pulse voltage of 13 kV, and the pulse repetition frequency of 1200 Hz. Figure S4 represents the time-dependent changes in the density of the main reactive species during ammonia synthesis by nanosecond pulse plasma. The solid lines in the figures represent the initial reactants N\({}_{2}\), H\({}_{2}\), and the product NH\({}_{3}\), respectively. In each discharge cycle, the species density shows a periodic pattern. Within a discharge cycle, the number of active particles increases at the onset of discharge due to the energy provided by the discharge, leading to the ionization and dissociation of the initial reactants into intermediate active species. During the intervals between discharges, the active particles and radicals lose external energy, leading to a reduction reaction and a decrease in density. Within a single pulse discharge, there is significant variability in the concentration of different particles. In previous studies, within systems containing only N\({}_{2}\) and H\({}_{2}\), the density of N typically ranged between 10\({}^{8}\) and 10\({}^{12}\) cm\({}^{-3}\), and the density of H between 10\({}^{10}\) and 10\({}^{16}\) cm\({}^{-3}\). However, after adding Ar, the density of N ranges between 10\({}^{10}\) and 10\({}^{18}\) cm\({}^{-3}\), and the density of H between 10\({}^{16}\) and 10\({}^{19}\) cm\({}^{-3}\) (compared under the same  
Figure 8: Effect of different Ar and He additions on rotational temperature. voltage conditions, as discharge voltage can alter particle density) [51]. This indicates that the involvement of Ar promotes the dissociation of N\({}_{2}\) and H\({}_{2}\). The lower density of N compared to H also suggests that the dissociation of N\({}_{2}\) is the rate-limiting step in the entire ammonia synthesis reaction. The intermediate species NH and NH\({}_{2}\) are at a lower magnitude, only increasing in particle density at the start of discharge, indicating that the ammonia synthesis reaction primarily occurs with the involvement of discharge plasma. According to the previous studies, N\({}_{2}\)+, N, and H* were considered as important initial reactants. NH\({}_{x}\) species were also considered as important intermediates [52; 53]. By facilitating a charge transfer reaction with N\({}_{2}\) (10), the introduction of Ar augmented the density of N\({}_{2}\)+ ions. A similar charge transfer process is observed between Ar+ and H\({}_{2}\) (11) [54]. Figure 9 shows the conversion between Ar and Ar+. As shown in Figure 9, the decrease in Ar particle density indicates that Ar is consumed throughout the reaction, Ar collides with electrons to produce Ar+ (12), and the reaction of Ar+ with N\({}_{2}\) and H\({}_{2}\) increases the particle density of N\({}_{2}\)+ and H\({}_{2}\)+. At the beginning of the discharge, as the charge transfer between Ar+ and N\({}_{2}\) and H\({}_{2}\) is reduced to Ar, and the particle density of Ar increases, but is always lower than in the previous discharge cycle. The effect of different additions of Ar on the rate of the charge transfer reaction is shown in Figure 10. Adding Ar leads to a higher rate of the charge transfer reaction, suggesting a rise in the likelihood of inelastic collisions. This is indicative of elevated densities of N\({}_{2}\)+ and H\({}_{2}\)+, a finding that aligns with the OES outcomes presented in Figure 7b. In addition to the enhanced electron collision reaction, the enhancement of the Penning excitation and ionization reactions also leads to enhanced N\({}_{2}\) dissociation.