# Cryogenic System for FTIR Analysis of Hydrocarbon Fuels at Low Temperature and Atmospheric Pressure
## 3 Results
### FTIR Spectroscopy Data of Hydrocarbon Samples Obtained Using the Cryogenic System  
Figure 6 shows the results of the experiment with CH\({}_{3}\)OH methanol and obtaining its spectra. Key characteristic peaks corresponding to the vibrational modes of methanol functional groups can be observed, in particular CH\({}_{3}\) bending in the range of 1450-1550 cm\({}^{-1}\), C-H stretching in the range of 2840-2860 cm\({}^{-1}\), and O-H stretching in the range 3200-3350 cm\({}^{-1}\). These bands correspond to key IR peaks of methanol, in particular alcohol and hydrocarbon groups. Also, there is a comparison of our data with results of other authors in this field in Table 3. Assignments discovered in their works mostly correspond with our data, in particular CH\({}_{3}\) bending, C-H stretching, and O-H stretching vibrations, although they have been obtained under vacuum and in almost the same temperature range. As for Figure 7--C-H bending characteristic peaks of kerosene are also present--out-of-plane vibration in the range of 800-950 cm\({}^{-1}\) and scissoring vibration in the range of 1500-1700 cm\({}^{-1}\). Comparison with other authors' results is provided in Table 4. All data correlate well. C-H bending peaks are good examples of the activity of kerosene functional groups while being exposed to IR radiation, since they exhibit intense vibrations in certain way. Slight broadening of the bending peaks seen in the Figure 7 and Table 4 is due to a hypsocromic shift, the occurrence of which can be explained by the method of obtaining solid kerosene (80-100 K), since it was gradually cooled from room temperature (300 K) from liquid phase at atmospheric pressure. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**\(\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{\mathbf{ }}}}}}}}}}}}}}\)****} & **Uncertainty** & **Type** & **Units** & **Standard** & **Distribution** & **Standard** & **Sensitivity** & **Uncertainty** \\  & **Source** & & & **Error** & & **Uncertainty** & **Coefficient** & **Contribution, K** \\ \hline \multirow{2}{*}{3.} & Temperature & & & & & & & \\  & gradient in bar & A & K & \(\pm\)0.27 & Rectangular & \(\frac{\pm 0.27}{\sqrt{3}}\) & 1 & \(\pm\)0.156 \\ \hline \multirow{2}{*}{4.} & PID controller & & & & & & & \\  & fluctuation & B & K & \(\pm\)0.10 & Normal & \(\pm\)0.1 & 1 & \(\pm\)0.100 \\ \hline \multicolumn{7}{c}{Total standard uncertainty} & & & & & \(\pm\)0.358 \\ \hline \multicolumn{7}{c}{Expanded uncertainty} & & & & \(\pm\)0.716 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: _Cont._  
Figure 6: Methanol characteristic peaks at low temperatures. There is a comparison of the characteristic peaks of ethanol C\({}_{2}\)H\({}_{5}\)OH functional groups in Table 5, in particular C-H and O-H stretching vibrations; all data show good correlation. This stretching highlights the important alcohol and hydrocarbon components of the ethanol molecule, which exhibit dynamic behavior in response to IR radiation. Those peaks and comparisons prove the usability and reliability of the setup and measurement technique. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \(\mathbf{\mathcal{N}}\) & **Authors** & **Temperature, Type** & **Pressure, Type** & \
\begin{tabular}{c} **C-H Bending** \\ **(Rocking and** \\ **Out-of-Plane), cm\({}^{-1}\)** \\ \end{tabular} &
\begin{tabular}{c} **C-H Bending** \\ **(Sicssoring), cm\({}^{-1}\)** \\ \end{tabular} \\ \hline
1. &
\begin{tabular}{c} [PERSON], [PERSON] \\ et al. [23] \\ \end{tabular} & Room & Vacuum & 800 & 1300–1500 \\ \hline
2. &
\begin{tabular}{c} [PERSON], and [PERSON] [24] \\ \end{tabular} & Room & Vacuum & 650–800 & 1300–1500 \\ \hline
3. &
\begin{tabular}{c} [PERSON], \\ [PERSON] et al. [25] \\ \end{tabular} & Room & Vacuum & 800 & 1500 \\ \hline
4. &
\begin{tabular}{c} Our results \\ \end{tabular} & Low (80–100 K) & Atmospheric & 800–950 & 1500–1700 \\ \hline \hline \end{tabular}
\end{table}