## 3 Results and Discussion
### Effect of Thermal Evolution on Raman Spectra of Coal  
Two distinct regions of Raman frequency vibrations can be seen in Figure 3 (after baseline correction), namely the D-spectral band peak located at 1350 cm\({}^{-1}\). nearby and the G-spectral band peak at 1585 cm\({}^{-1}\). nearby.  
In order to better compare and analyze the parameters such as the integral intensity, FWHM, and peak position difference of the D and G peaks of the magmatic thermal evolution coal samples and normal coal samples for this study, the fitted curves of the Raman spectrograms were obtained by using the Origin 2022b software and fitting the data to the peaks using the combination method IX, found by [PERSON] et al. [49] (taking DX 1# and DX 2# as examples), as shown in Figure 4.  
Because the FWHM of the D band has good correlation with the disordered degree of carbonaceous materials [50] and the half-peak width of the G band can reflect graphitization very sensitively [51], the FWHM ratio (F\({}_{\text{D1}}\)/F\({}_{\text{G}}\)) of the D and G bands was used as a study parameter. In an effort to better study the magmatic thermal evolutionary effects on the molecular structure of low-rank coals, the ratio of the integral intensity of the peaks in the D and G bands (I\({}_{\text{D1}}\)/I\({}_{\text{G}}\)) was also used as a study parameter to analyze the degree of structural orderliness.  
Figure 3: The Raman spectra of magmatic thermal evolution coal samples and normal coal samples.  
Based on the results of the split-peak fitting in the 1000-2000 cm\({}^{-1}\). range, the obtained characteristic parameters in terms of the G and D\({}_{1}\) peak positions, the peak position difference (G-D\({}_{1}\)), and the integral intensity ratio (I\({}_{\text{D1}}\)/I\({}_{\text{G}}\)) are shown in Table 3.  
As can be seen from Table 3, the Raman shift of the D\({}_{1}\) peak of the experimental coal sample varies from 1339 to 1346 cm\({}^{-1}\); the Raman shift of G peak varies from 1576 to 1589 cm\({}^{-1}\).; the maximum value of the peak difference (G-D\({}_{1}\)) is 249 cm\({}^{-1}\). and the minimum value is 230 cm\({}^{-1}\). The peaks and peak differences are relatively close, showing that the structure of order in the magmatic thermally evolved coal samples and normal coal samples are relatively similar. A cross-sectional comparison of the magmatic thermally evolved coal samples and the normal coal samples of the same coal mine reveals that the D\({}_{1}\) and G peak positions of each experimental coal sample are shifted to some extent, and the G-D\({}_{1}\) values of the magmatic thermally evolved coal samples, DX 1# and HY 1#, are larger than those of the normal coal samples, i.e., the thermally evolved coal samples have a lower disordered structure than the normal coal samples [13; 52]. The I\({}_{\text{D1}}\)/I\({}_{\text{G}}\) ranges from 1.55 to 2.16, and the F\({}_{\text{D1}}\)/F\({}_{\text{G}}\) ranges from 2.16 to 2.36. The I\({}_{\text{D1}}\)/I\({}_{\text{G}}\) and F\({}_{\text{D1}}\)/F\({}_{\text{G}}\) values of the thermally evolved coal samples are smaller than those of the normal coal samples, indicating that the internal macromolecular defects of the DX 1# and HY 1# coal samples are of a lower degree and higher degree of graphitization, i.e., magmatic thermal evolution promoted the generation of the internal ordered structure of the low-rank coal. The trend of the value of La in the Raman spectra is consistent with that of the XRD, so it will not be repeated.