## 3 Results and Discussion
### Spectroscopic Characterization
#### 3.3.1 Detected Species in Plasma
It must be noted that the presented results were at various voltages from 10.5 to 14.5 kV and the frequency of 50 Hz for the fixed power electrode with a 1 sLm gas flow rate, at different frequencies from 9000 to 18,000 rpm for the rotating power electrode with 14 kV and 50 Hz as long as at a 1 sLm gas flow rate, and at different gas flow rates for 14 kV and 50 Hz at 18,000 rpm in atmospheric pressure and a spectral wavelength range of 200-1000 nm. As can be seen from Figure 9a, the intensities of all lines were increased with more voltage applied to the discharge medium. The growing voltage produced a rise in the electric field between the electrodes and the acceleration of electrons. The production of species by the reactions of Equation (5) and its excitation was also increased. The intensity of the emission line of C\({}_{2}\) was reduced by increasing the rotation frequency of the power electrode, unlike the other intensities that were raised (see Figure 9b). The growth of intensities was because the contact of the LPG gas with the filaments was higher when the electrode was rotating [2]. The formed C\({}_{2}\) molecules were a stable species which recombine together to form carbon clusters. The formed carbon clusters diffused  
Figure 8: Scheme of the dissociation of C\({}_{4}\)H\({}_{10}\)/C\({}_{3}\)H\({}_{8}\) molecules by electron collisions. Figure 9: The normalized intensities of generated species in the plasma discharge versus (**a**) different voltages applied on the stationary power electrode at 1 sLm gas flow rate, (**b**) rotational frequencies of the power electrode at 14 kV applied voltage and 1 sLm gas flow rate, and (**c**) gas flow rates at 14 kV applied voltage and 18,000 rpm rotation frequency of the power electrode. in all directions and then deposited on the electrodes and on the walls of the discharge tube [18]. This process was enhanced with the higher rotation frequency of the electrode. On the other hand, similarly to the consumed power, the intensity of emission lines of all species decreased with the gas flow rate (see Figure 9c). The axial transport of energy by the gas flow produced a diminishment of the energy of electrons and heavy particles. Therefore, the formation and excitation of species in the plasma also dropped. It should be also mentioned that the dependence of the intensity of C\({}_{2}\) and H\({}_{2}\) bands with the conditions was similar to the H\({}_{2}\) and C\({}_{2}\) selectivities obtained by the GC of the exhaust gas, showing that we were observing the formation of these species inside the filament. The OES permitted us also to characterize the plasma produced in this reactor. In our case, the lines corresponding to hydrogen and carbon were of enough intensity to determine the main plasma parameters, such as the electron density and temperatures of the electrons and heavy particles by different spectroscopic methods. The values of these parameters define the kinetic of the plasma and the transformation of LPG gas to H\({}_{2}\) gas. As a discharge dominated by the electron kinetic, where the dissociation reactions of Equation (5) are given by the collisions with electrons, the number of electrons given by the electron density determine the efficiency of the LPG conversion. The values of the electron density can be obtained by analyzing the Stark broadening of atomic lines. In this work, where intense lines of hydrogen atoms were detected, the broadening of the H\({}_{\alpha}\) line was used (Section 3.3.4). The kinetic of reactions in the plasma discharge (Equation (5)) depend also on the energy of these electrons, that is, the electron temperature. Electrons pick the energy directly from the electric field and share it with the rest of the particles by collisions, producing their excitation and ionization. Then, the population of excited states is given by the electron temperature. In the case of the equilibrium condition, the distribution function of excited states follow the distribution of Boltzmann with a temperature equal to the electron temperature.