## 3 Results and Discussion
### Spectroscopic Characterization
#### 3.3.1 Detected Species in Plasma  
In the plasma, the electron and heavy particles collision processes excite several plasma species to the upper states decaying and emitting photons with different wavelengths. Through recording of the emission spectra of the plasma discharge medium, these photons can be detected and analyzed. In this work, the OES technique was used to identify the different produced reactive species in the C\({}_{4}\)H\({}_{10}\)/C\({}_{3}\)H\({}_{8}\) gas in the developed plasma reactor. Figure 7 shows the recorded emission spectra for the spectral wavelength range of 200-1000 nm for the plasma reactor at atmospheric pressure with the C\({}_{4}\)H\({}_{10}\)/C\({}_{3}\)H\({}_{8}\) gas mixture, a 14 kV AC applied voltage, a motor rotation frequency (power electrode) of 18,000 rpm, and a gas flow of 1 sLm. The identified lines have been highlighted in this figure and presented in Table 2 together their main data. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Species** & \(\mathbf{\lambda}\)**(nm)** & **Transition Name** & **Transition Symbol** \\ \hline
**NO (\(\mathbf{\gamma}\))** & 200–300 & Molecular Transition & \(A^{2}\Sigma\to X^{2}\Pi\) \\ \hline
**OH (Q)** & 306–312 & Molecular Transition & \(A^{2}\Sigma\to X^{2}\Pi\) \\ \hline \multirow{4}{*}{**CO\({}_{2}\)**} & 326.1 & Fox, Duffendack and Barker’s System & \(X^{2}\Pi_{g}\to A^{2}\Pi_{u}\) \\ \cline{2-4}  & 338.3 & Fox, Duffendack and Barker’s System & \(X^{2}\Pi_{g}\to A^{2}\Pi_{u}\) \\ \cline{2-4}  & 368.2 & Fox, Duffendack and Barker’s System & \(X^{2}\Pi_{g}\to A^{2}\Pi_{u}\) \\ \cline{2-4}  & 407.3 & Fox, Duffendack and Barker’s System & \(X^{2}\Pi_{g}\to A^{2}\Pi_{u}\) \\ \hline
**NH** & 336.5 & Molecular Transition & \(A^{3}\Pi\to X^{3}\Sigma^{-}\) \\ \hline \multirow{2}{*}{**CN**} & 385–388 & Violet Band System & \(B^{2}\Sigma^{+}\to X^{2}\Sigma^{+}\) \\ \cline{2-4}  & 762.3, 790.9 & Molecular Transition & \(A^{2}\Pi\to X^{2}\Sigma\) \\ \hline \multirow{4}{*}{**CH**} & 314.5 & Molecular Transition & \(C^{2}\Sigma^{+}\to X^{2}\Pi\) \\ \cline{2-4}  & 389.1 & Molecular Transition & \(B^{2}\Sigma^{-}\to X^{2}\Pi\) \\ \cline{2-4}  & 427–432 & Molecular Transition & \(A^{2}\Delta\to X^{2}\Pi\) \\ \hline H\({}_{\varepsilon}\) & 397.1 & Atomic Transition & \(7\to 2\) \\ \hline H\({}_{\delta}\) & 410.05 & Atomic Transition & \(6\to 2\) \\ \hline H\({}_{\gamma}\) & 434.01 & Atomic Transition & \(5\to 2\) \\ \hline H\({}_{\beta}\) & 486.1 & Atomic Transition & \(4\to 2\) \\ \hline H\({}_{\alpha}\) & 656.2 & Atomic Transition & \(3\to 2\) \\ \hline H\({}_{2}\) & 627–637 & Fulcher Band System & \(X^{1}\Sigma_{g}\to C^{1}\Pi_{u}\) \\ \hline \multirow{2}{*}{**C\({}_{2}\)**} & 473.4 & Swan Band System & \(d^{3}\Pi_{g}\to a^{3}\Pi_{u}\) \\ \cline{2-4}  & 516.4 & Swan Band System & \(d^{3}\Pi_{g}\to a^{3}\Pi_{u}\) \\ \cline{2-4}  & 560.1 & Swan Band System & \(d^{3}\Pi_{g}\to a^{3}\Pi_{u}\) \\ \hline \end{tabular}
\end{table} 
Table 2: Parameters of the atomic lines and molecular bands detected by OES in the rotating electrode AC plasma reactor [16; 17]. Figure 7: Example of the emission spectrum detected for the rotating electrode AC plasma reactor with the main identified lines at applied voltage of 14 kV, rotation frequency of 18,000 rpm, and gas flow rate of 1 sLm. The most recognized spectra in these figures are H\({}_{2}\), C\({}_{2}\), and CH bands that are directly produced by the dissociation of the propane and butane molecules by the following reactions [13; 18; 19]:  
\[ \begin{array}{c}2\mathrm{C_{4}H_{10}+e\to C_{2}+2C_{3}H_{8}+2H_{2}+e}\\ \mathrm{C_{3}H_{8}+e\to C_{2}H_{4}+CH_{4}+e}\\ \mathrm{C_{3}H_{8}+e\to C_{3}H_{6}+H_{2}+e}\\ \mathrm{C_{2}H_{4}+e\to C_{2}H_{2}+H_{2}+e}\\ \mathrm{2 CH_{4}+e\to C_{2}+4H_{2}+e}\\ \mathrm{C_{3}H_{6}+e\to C_{2}H_{2}+CH_{4}+e}\end{array}  \tag{5}\]  
The Balmer lines of hydrogen were also detected. It is obvious that the amount of H\({}_{2}\) produced in all the above reactions was higher than in the carbon one. The theoretical ratio between the H\({}_{2}\) and C\({}_{2}\) production was 9/3.5.