## 3 Results and Discussion
### Model Results
#### 3.2.4 Co\({}_{2}\) Splitting  
The high values of electron density and temperature indicate that the chemistry in the AC-PPP reactor was dominated by the collisions of electrons with CO\({}_{2}\) ground state molecules. As predicted by the model, the most relevant mechanisms of CO\({}_{2}\) splitting were:  
* the electron impact dissociation (or dissociative de-excitation collision) producing CO and O (see reactions 7 and 9 in Table 1),
* the electron ionization producing CO\({}_{2}\)\({}^{+}\) ions (see reaction 12 in Table 1),
* the electron dissociative attachment producing CO molecules and O\({}^{-}\) ions (see reaction 15 in Table 1). These mechanisms align with those proposed by [PERSON] et al. [48] for pure CO\({}_{2}\) splitting. The energy required by these three processes is higher than that needed for splitting by C=O bound breaking (CO\({}_{2}\)\(\rightarrow\) CO\(+\)\(\frac{1}{2}\)O\({}_{2}\)), i.e., 279.8 kJ/mol. This explains the low energy efficiency found for this plasma, i.e., lower than 6%. The distribution of the four formed species: CO\({}_{2}\)\({}^{+}\), CO, O, O\({}_{2}\), and O\({}^{-}\) were studied to identify the reactions that dominated in each part of the reactor. Figure 13 shows the spatial distribution of the density of CO\({}_{2}\)\({}^{+}\) ions formed for times, 2, 6, 10, 14, and 18 ms. In contrast with the electrons which moved toward the power electrode during the positive voltage applied (2, 6, and 10 ms) and were aggregated there, the electric field accelerated the produced positive ions CO\({}_{2}\)\({}^{+}\) in the direction of this field. If a CO\({}_{2}\)\({}^{+}\) ion obtains enough acceleration from the electric field, it collides with the background gas molecules and ionizes them. However, this phenomenon rarely happens in high electron density plasmas, where CO\({}_{2}\)\({}^{+}\) ions are less effective than the electrons in the impacting ionization process. As shown in Figure 13, the CO\({}_{2}\)\({}^{+}\) ions accumulated near the ground electrode during the positive voltage applied, and they accumulated in the powered electrode with the negative voltages. Figure 12: Spatial distribution of the electron temperature for times (**a**) 2 ms, (**b**) 6 ms, (**c**) 10 ms, (**d**) 14 ms, and (**e**) 18 ms for the reactor at 22 kV AC voltage and 1 cm distance between electrodes. The maximum values of the CO\({}_{2}\)+ density were found inside the metallic inlet/outlet pipes. The positive ions accumulated in this zone because they did not move toward the electrodes due to the low electric field inside the pipes. However, the CO\({}_{2}\)+ ion is an unstable species and will be quickly recombined with electrons or negative ions O\({}_{2}\)- to convert to CO and O, and/or O\({}_{2}\)[48]. Density of Neutral Species CO, O, and O\({}_{2}\)  
The densities of the neutral species CO and O generated inside the plasma discharge medium of the developed AC-PPP reactor at times 2, 6, 10, 14, and 18 ms are presented in Figures 14 and 15. These neutral species were produced near the powered electrode during the positive voltage and the ground electrode during the negative voltage. This was due to the high electron density near the electrodes, which produced the dissociation and attachment processes of the neutral species in these regions. The maximum values of CO and O densities are equal to \(4.7\times 10^{11}\) cm\({}^{-3}\) and \(2.3\times 10^{11}\) cm\({}^{-3}\), respectively. The maximum CO density is higher than O because this molecule is produced by two mechanisms, electron impact dissociation (reaction 7 and 9) and electron dissociative attachment (reaction 15). CO is a relatively stable molecule that can recombine with O and O\({}^{-}\) to form new CO\({}_{2}\) when the residence time is high [48]. However, the O atoms recombine quickly into oxygen molecules, O\({}_{2}\) and/or ozone, O\({}_{3}\).