## 3 Results and Discussion
### Spectroscopic Characterization
#### 3.3.1 Detected Species in Plasma
by the stoichiometric relationship. For each C\({}_{3}\)H\({}_{8}\) and C\({}_{4}\)H\({}_{10}\) mol converted, 9 moles of H\({}_{2}\) and 3.5 moles of C\({}_{2}\) were formed. The hydrogen atoms play an important role in increasing the ionization processes, hence the ignition to an active filamentary mode. An increase in the concentration of H and subsequently H\({}^{*}\) atoms led to an increase in the secondary ionization processes [13; 18]:  
\[ \begin{array}{c}\mathrm{H_{2}+e\to H+H+e}\\ \mathrm{H+e\to H^{+}+e+e}\\ \mathrm{H+e\to H^{+}+e}\\ \mathrm{H^{*}+e\to H^{+}+e+e}\end{array}  \tag{6}\]  
In this secondary ionization process, the hydrogen metastable state H\({}^{*}\), which has a relatively long lifetime up to 12 s, had an important contribution [2]. A scheme of the main mechanisms that produce the dissociation of C\({}_{4}\)H\({}_{10}\)/C\({}_{3}\)H\({}_{8}\) molecules in a kinetic dominated by the electron collisions is presented in Figure 8. \begin{table}
\begin{tabular}{c c c c} \hline
**Species** & **\(\boldsymbol{\lambda\ (nm)}\)** & **Transition Name** & **Transition Symbol** \\ \hline \multirow{4}{*}{**CO**} & 458.5 & The Triplet Bands & \(d^{3}\Delta\to a^{3}\Pi\) \\ \cline{2-4}  & 564.2 & The Triplet Bands & \(d^{3}\Delta\to a^{3}\Pi\) \\ \cline{2-4}  & 601.4 & The Triplet Bands & \(d^{3}\Delta\to a^{3}\Pi\) \\ \cline{2-4}  & 643.2 & The Triplet Bands & \(d^{3}\Delta\to a^{3}\Pi\) \\ \hline \multirow{4}{*}{**CO\({}^{+}\)**} & 427.3 & Comet-tail system (First Negative System) & \(X^{2}\Pi\to A^{2}\Sigma\) \\ \cline{2-4}  & 484.1 & Comet-tail system (First Negative System) & \(A^{2}\Pi\to X^{2}\Sigma\) \\ \hline \multirow{2}{*}{**O\({}_{2}\)**} & 385.3 & Chamberlains Airglow System & \(a^{1}\Delta_{g}\to\mathrm{C^{3}\Delta_{u}}\) \\ \cline{2-4}  & 406.2 & Molecular Transition & \(A^{3}\Sigma_{u}^{+}\to X^{3}\Sigma_{g}^{-}\) \\ \hline \multirow{2}{*}{**O\({}_{2}^{+}\)**} & 588.3, 602.5 & Molecular Transition & \(b^{4}\Sigma_{g}^{-}\to a^{4}\Pi_{u}\) \\ \cline{2-4}  & 777.1 & Atomic Transition & \(3\mathrm{p^{5}P}\to 3\mathrm{s^{5}S}\) \\ \cline{2-4}  & 843.2 & Atomic Transition & \(3\mathrm{p^{3}P}\to 3\mathrm{s^{5}S}\) \\ \hline \multirow{2}{*}{**N\({}_{2}^{+}\)**} & 391.05 & Second Negative System & \(B^{2}\Sigma_{u}^{+}\to X^{2}\Sigma_{g}^{+}\) \\ \cline{2-4}  & 357.2, 380.2 & Second Positive System & \(\mathrm{C^{3}\Pi_{u}\to B^{3}\Pi_{g}}\) \\ \cline{2-4}  & 664.1, 672.4, 683.2 & First Positive System & \(B^{3}\Pi_{g}\to A^{3}\Sigma_{u}^{+}\) \\ \cline{2-4}  & 968.3, 994.1 & First Positive System & \(B^{3}\Pi_{g}\to A^{3}\Sigma_{u}^{+}\) \\ \hline \multirow{4}{*}{**N**} & 740–750 & Atomic Transition (3-lines Multiplet) & \(3\mathrm{s^{4}P}-3\mathrm{p^{4}S^{0}}\) \\ \cline{2-4}  & 815–825 & Atomic Transition (7-lines Multiplet) & \(3\mathrm{s^{4}P}-3\mathrm{p^{4}P^{0}}\) \\ \cline{1-1} \cline{2-4}  & 855–875 & Atomic Transition (8-lines Multiplet) & \(3\mathrm{s^{4}P}-3\mathrm{p^{4}D^{0}}\) \\ \hline \end{tabular}
\end{table} 
Table 2: _Cont._The detection of N\({}_{2}\), NH, CO\({}_{2}\), CO, and CN bands confirmed the existence of nitrogen and oxygen in the discharge tube. The reactions of the oxygen, hydrogen, and nitrogen of air with the carbon produced in the LPG dissociation explain the detected species [16; 19]. These species could have been coming from the air entrance by the bottom part, impurities of the LPG gas and sputtering of the dielectric polyamide layer. The gas chromatography analysis of the exhaust gas showed that the concentration of these species was lower than 3% and did not have a big influence on the plasma kinetic. Figure 9 shows the normalized intensities of the band heads and the maximum of atomic lines obtained by the emission spectra of the plasma reactor with the C\({}_{4}\)H\({}_{10}\)/C\({}_{3}\)H\({}_{8}\) gas mixture in two respective stages, namely, the stationary and rotating power electrodes.