## 3 Results and Discussion
### Influence of Thermal Evolution on FTIR spectroscopy Characteristics of Functional Groups in Coal  
The FTIR spectra for the four coal samples are depicted in Figure 5. Various functional groups in coal exhibit distinct vibrational frequencies, corresponding to specific charac  
Figure 4: (**a**) Raman spectrum of DX 1# coal samples with the corresponding curve fitted bands; (**b**) Raman spectrum of DX 2# coal samples with the corresponding curve fitted bands. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Sample** & **Peak** & **Position (cm\({}^{-1}\))** & **Integral Intensity** & **FWHM** & **I\({}_{\text{D1}}\)/I\({}_{\text{G}}\)** & **G-D\({}_{1}\)** & **F\({}_{\text{D1}}\)/F\({}_{\text{G}}\)** & **L\({}_{\text{a}}\) (Å)** \\ \hline DX 1\# & G & 1576 & 87,938 & 74 & 1.84 & 236 & 2.16 & 26.93 \\ DX 2\# & G & 1576 & 208,233 & 76 & & & & \\ D\({}_{1}\) & 1346 & 449,889 & 179 & 2.16 & 230 & 2.36 & 22.94 \\  & G & 1588 & 162,252 & 70 & & & & \\ HY 1\# & D\({}_{1}\) & 1339 & 251,734 & 153 & 1.55 & 249 & 2.19 & 31.97 \\  & G & 1589 & 135,348 & 74 & & & & \\ HY 2\# & D\({}_{1}\) & 1343 & 252,906 & 164 & 1.87 & 246 & 2.22 & 26.50 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Parameters of the fitted peaks of the Raman spectra of coal samples. teristic absorption peaks in the infrared spectrum [53] (as detailed in Table 4). The FTIR spectra of coal can be categorized into four sets of absorption peaks: hydroxyl absorption peaks within the wavenumber range of 3700-3000 cm\({}^{-1}\), aliphatic absorption peaks spanning 3000-2700 cm\({}^{-1}\)., absorption peaks associated with oxygenated functional groups in the range of 1800-1000 cm\({}^{-1}\)., and absorption peaks reflecting the structure of aromatic compounds within the range of 900-700 cm\({}^{-1}\). [54]. Figure 5 depicts that there are multiple absorption peaks in the infrared spectra of each experimental coal sample, indicating the existence of complex functional group structures in coal. The infrared spectra of the magmatic thermal evolution coal samples and the normal coal samples partly have the same characteristics, but there are also some differences: there are no obvious characteristic peaks in each coal sample in the 2700-1800 cm\({}^{-1}\). band, and there are absorption peaks in other bands; the location, sharpness, and width of peaks near \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Number**} & \multirow{2}{*}{**Peak Position**} & \multicolumn{2}{c}{**Wavenumber**} & \multirow{2}{*}{**Functional Group Assignment**} \\  & & **Range** & & \\ \hline
1 & 3680 & 3685–3600 & Free -OH \\
2 & 3550 & 3600–3500 & -OH self-contained hydrogen bond \\
3 & 3400 & 3550–3200 & -OH stretching vibration \\
4 & 2950 & 2975–2950 & CH\({}_{3}\) asymmetric stretching vibration \\
5 & 2920 & 2935–2915 & CH\({}_{2}\) asymmetric stretching vibration \\
6 & 2870 & 2875–2860 & CH\({}_{3}\) symmetric stretching vibration \\
7 & 2850 & 2860–2840 & CH\({}_{2}\) symmetric stretching vibration \\
8 & 1750 & 1770–1720 & Aliphatic C=O stretching vibration \\
9 & 1700 & 1715–1690 & Aromatic C=O stretching vibration \\
10 & 1675 & 1690–1660 & C=O stretching vibration in quinone \\
11 & 1600 & 1605–1595 & Aromatic C=C stretching vibration \\
12 & 1470 & 1480–1465 & CH\({}_{2}\) asymmetric deformation vibration \\
13 & 1440 & 1460–1435 & CH\({}_{3}\) asymmetric deformation vibration \\
14 & 1380 & 1385–1370 & CH\({}_{3}\) symmetric bending vibration \\
15 & 1150 & 1160–1120 & C=O-C stretching vibration \\
16 & 1110 & 1120–1080 & Se-SO stretching vibration \\
17 & 1050 & 1060–1020 & Si-O-Si or Si-O-C stretching vibration \\
18 & 870 & 900–850 & aromatic nucleus (CH), one adjacent H deformation \\
19 & 820 & 825–800 & aromatic nucleus (CH), three adjacent H deformation \\
20 & 750 & 770–730 & aromatic nucleus (CH), five adjacent H deformation \\
21 & 720 & 724–716 & n-Alkane side-chain skeleton (CH\({}_{2}\))\({}_{n}\) oscillatory vibration \\ \hline \hline \end{tabular}
\end{table}