## 3 Results  
### Spectroscopic Investigations  
Figure 1 presents the concentrations of seven detectable reaction products of the ASPNC process. The level of the O\({}_{2}\) or CO\({}_{2}\) admixture is given as a fraction of the feed gas on the x-axis, as well as an equivalent concentration as a dashed line in the respective figure. In the pure nitrogen-hydrogen feed gas, i.e., without admixture of O\({}_{2}\) or CO\({}_{2}\), HCN is the most abundant reaction product, followed by CO, C\({}_{2}\)H\({}_{2}\), NH\({}_{3}\), and CH\({}_{4}\). Oxygen was present due to impurities in the technical precursor gas, leakage in the vacuum reactor,or sources from the steel surface of the model probe, and was primarily detected after its reaction to CO. Both O\({}_{2}\) and CO\({}_{2}\) were dissociated in the reactor under the release of oxygen, which can react to further chemical compounds. As a result, the fundamental dependencies of the species concentrations towards the oxygen-containing precursor gases were comparable. For CO\({}_{2}\), the degree of dissociation was about 74%. This reduces the concentrations of reactive chemical compounds, such as HCN or C\({}_{2}\)H\({}_{2}\). Additionally, the high affinity of hydrogen to oxygen led to the formation of H\({}_{2}\)O. By increasing the O\({}_{2}\) or CO\({}_{2}\) admixture in the nitrogen-hydrogen feed gas, the concentrations of the oxygen-containing species were monotonically increased, and more of the sputtered carbon reacted to form stable species CO and CO\({}_{2}\), and did not participate in formation of hydrocarbons and CN-species. Therefore, concentrations of HCN, CH\({}_{4}\), and C\({}_{2}\)H\({}_{2}\) were monotonically decreased, while NH\({}_{3}\) was slightly increased due to the proposed reaction paths as follows [26]:  
\[2\cdot\mathrm{C_{x}H_{y}}+0.5\cdot\mathrm{(4x+y)}\cdot\mathrm{O_{2}}\to 2 \times\mathrm{CO_{2}}+y\cdot\mathrm{H_{2}O} \tag{1}\]  
\[\mathrm{HCN}+0.5\cdot\mathrm{O_{2}}\to\mathrm{HNCO} \tag{2}\]  
\[\mathrm{HNCO}+\mathrm{H_{2}O}\to\mathrm{NH_{3}}+\mathrm{CO_{2}} \tag{3}\]  
As an intermediate product, HCNO decomposed to NH\({}_{3}\) and CO\({}_{2}\). At higher oxygen contents above 7%, CO becomes the species with the highest concentration. In addition, more hydrogen formed H\({}_{2}\)O, resulting in a decreased NH\({}_{3}\) concentration. The normalized oxygen distribution in the reactive species CO, CO\({}_{2}\), and H\({}_{2}\)O is shown in Figure 2 in which 100% corresponds to the amount of oxygen that was fed into the reactor. For both O\({}_{2}\) and CO\({}_{2}\), at a low flow rate, it is apparent that the sum of all oxygen-containing species is well above 100%, which can be attributed to the leakage and contamination of reactor parts only. As a result, more oxygen is present and bonds preferentially as CO. As Figure 2a shows, H\({}_{2}\)O and CO\({}_{2}\) were detectable only at O\({}_{2}\) admixtures larger than 3%, with their concentrations remaining close to their limits of detection even at high levels of admixture. The sum of the above-mentioned oxygen-containing species falls below 100% for more than 3% O\({}_{2}\) admixture. The likely reason is the degree of dissociation of oxygen and the contamination of the reactor. With an increased O\({}_{2}\) concentration, leakage becomes less important, whereas the degree of dissociation of O\({}_{2}\) might be regarded as relatively constant or even decreasing resulting in saturation at about 70%. However, no statement can be made about the degree of dissociation by means of IRLAS, since O\({}_{2}\) cannot  
Figure 2: Normalized atomic oxygen contributions of the oxygen-containing species (CO, CO\({}_{2}\), and H\({}_{2}\)O) and their sum related to the oxygen content in the precursor gas for (**a**) O\({}_{2}\) and (**b**) for CO\({}_{2}\). \(T=540\)\({}^{\circ}\)C, N\({}_{2}+\)O\({}_{2}=90\%\) or N\({}_{2}+\)CO\({}_{2}=90\%\), H\({}_{2}=10\%\), \(P_{\mathrm{AS}}=6.0\) kW. be measured spectroscopically in the infrared range.