## 1 Introduction  
Magma intrusion into coal seems is a common phenomenon in major coal-producing countries worldwide [1; 2]. Such intrusion results in the formation of more pronounced pore fissures within coal, leading to an increase in gas reservoir space, enhanced gas adsorption, and an elevated risk of spontaneous combustion [3], as well as coal and gas outbursts, all of which significantly impact the safety of coal mining [4; 5]. Through an analysis of coal and gas outburst accidents in coal mines, it has been discovered that the proximity of magma intrusion areas is the leading cause of outburst incidents [6; 7; 8]. The intrusion of magma alters the molecular structure of coal, consequently influencing the physical and chemical properties of the coal [9; 10; 11]. Typically, coal is primarily characterized as a porous material consisting of complex organic polymers and inorganic compounds. The internal microstructure of coal, including aromatic compounds, functional groups, and side chains, among others, to a certain extent, influences both the microscopic pore characteristics of coal and the adsorption/desorption properties of gas [12; 13; 14; 15; 16]. Therefore, it is necessary to study the thermal evolutionary effects of magma on the molecular structure of coal bodies, thus providing a molecular-scale theoretical basis for studying the effects of magma intrusion on the pore characteristics and gas adsorption/desorption of coal. The complex molecular structure of coal is a three-dimensional network of condensed aromatic rings and hydrogenated aromatic rings connected with various functional groups through various bridge bonds [12]. Analytical techniques such as X-ray diffraction (XRD), Raman spectroscopy, and Fourier transform infrared (FTIR) spectroscopy are widely used to study the molecular structural properties of coal [13; 15]. XRD can be applied to determine the physical structure of crystals and is also widely used to characterize the physical structure of non-crystals. In recent years, XRD has been used for characterizing the three-dimensional carbon-infilled structure of coal [14]. Raman spectroscopy belongs to scattering spectroscopy and is widely used for characterizing carbonaceous materials' crystal structure and the macromolecular structure of coal [17; 18; 19; 20; 21]. The Raman signal of graphite-like structures is most obvious in the first-order mode with D peaks and G peaks. The existence of D peaks is because of the existence of a large amount of heteroatoms or molecular lattice defects inside the coal, and the G peak is the only graphite-like characteristic spectral peak within the first-order Raman spectral curve, characterizing the degree of ordering of the microcrystalline structure [22; 23]. Scholars usually use G-D\({}_{1}\) and D\({}_{1}\)/G to assess information on the orderliness and crystallinity in carbon-containing materials, and use the intensity ratio of the D\({}_{1}\) band to the G band to estimate the average lateral sizes (L\({}_{a}\)) [20; 24; 13]. FTIR spectroscopy is widely used for studying the functional group components of coal, as well as for studying the coal rock composition and the degree of coalification [15; 25; 26; 27]. This technique has the capability to characterize the hydrocarbon structure and heteroatomic functional groups in coal by discerning changes in the position of each distinct absorption peak in the infrared spectrogram. At present, studies on the molecular structure of coal bodies mainly focus on magma contact metamorphic coals, with few studies on the differences in molecular structure between coal samples affected by magmatic heat and normal coal samples [9; 28; 29; 30]. Therefore, to comprehend the impact of magmatic thermal evolution more clearly on the molecular structure of coal, magmatic thermal evolution coal samples affected by magma intrusion as well as unaffected normal coal samples from Tiefa Daxing coal mine and Shenyang Hongyang No. 2 mine were used in this paper.