## 3 Results and Discussion
### Physical and Chemical Degradation
#### 3.2.2 FTIR Spectral Characterization and FTIR Indices  
The detailed FTIR band assignments are listed in Table 1. The assignments were performed in line with previous works [93; 94; 95; 96; 97; 98; 99; 100]. The 3500-500 cm\({}^{-1}\) spectral region of the FTIR spectra of the ancient wood sample is displayed in Figure 5a. \begin{table}
\begin{tabular}{c c} \hline \hline
**FTIR Band (cm\({}^{-1}\))** & **Band Assignment** \\ \hline
3337 & O-H stretching of intermolecular hydrogen bonds \\
2979 & Asymmetric CH stretch of the methoxy group of lignin \\
2943 & Asymmetric CH stretching of CH\({}_{2}\) groups of lignin, cellulose, hemicellulose \\
2914 & Symmetric CH stretching of CH\({}_{3}\) groups of lignin, cellulose, hemicellulose \\
1726 & C=O stretching of acetyl and carbonyl groups in hemicellulose \\
1590 & Skeletal vibrations of the aromatic ring, together with C=O stretch in lignin \\
1508 & C=C skeletal vibrations of the aromatic ring in lignin \\
1448 & Aromatic C-H deformation in lignin and carbohydrates \\
1429 & C-H in-plane deformation in lignin and carbohydrates \\
1376 & CH bending in cellulose, hemicellulose and lignin \\
1264 & Aromatic C-O stretching vibrations of methoxyl and phenyl propane guaiacol ring \\
1233 & Stretching vibrations of C-O in Xylene and syringyl ring \\
1157 & Asymmetric bridge C-O-C stretch mode in carbohydrates \\
1108 & Asymmetric in-plane aromatic skeletal stretching, C-C and C-O stretching \\
1054 & C-O stretching \\
1029 & Aromatic C-H in-plane deformation, and C-O deformation in primary alcohols \\
898 & Aromatic C-H out-of-plane ring deformations of cellulose \\
851 & Ring vibrations \\ \hline \hline \end{tabular}
\end{table} 
Table 1: FTIR band assignment of the wood samples. The FTIR indices for lignin, carbohydrates/lignin and Crystallinity (Table 2) were calculated on the basis of six absorption bands (Table 1). Specifically, the intensities of lignin peaks at \(\sim\)1590 cm\({}^{-1}\) and \(\sim\)1508 cm\({}^{-1}\) were chosen as lignin references as they are due to the aromatic skeletal vibration (C=C) in lignin [64]. Moreover, the band at \(\sim\)1730-1700 cm\({}^{-1}\) was chosen as a reference for carbohydrate, as it possesses no contribution from lignin. The lignin index (1\({}_{1596}\)/1\({}_{1505}\)) provides information on the molecular structure of aromatic lignin, while the carbohydrate/lignin index indicates the state of preservation of the carbohydrate content of wood [101]. The crystallinity index of wood cellulose in the sample was determined by calculating the I\({}_{1376}\)/I\({}_{2914}\) ratio [67]. This index is particularly useful for understanding structural changes in lignin, especially in archaeological wood. An increase in this ratio suggests the oxidation of aromatic lignins, the loss of guiaacyl units or, more likely, the demethylation of guiaacyl units [96; 102]. Since lignin index refers to the extent of possible oxidation of aromatic lignin and formation of free phenol groups [88; 96], it is therefore useful in revealing the state of ancient wood as some of the degradation products in aged lignin, such catechols, can result from fungal degradation [88; 96]. In the present work, among the different indexes, the lignin one was the highest in the examined sample (Table 2), indicating selective decomposition within the wood's lignin structure. This suggests the oxidative breakdown of lignin aromatic rings rather than complete lignin loss, leading to increased brittleness and reduced structural integrity [102]. Moreover, the lignin index value (4.040) is comparable to those of fresh wood standard (\(\sim\)1.5-2.0) [103]. The high lignin index found in this work suggests a relative enrichment of lignin content. This is indeed common in archaeological wood because cellulose and