# Spectral Raman Database of Modern Acrylic Paints at 532 nm and 633 nm Laser Excitation Wavelengths
## 3 Results and Discussion
The Raman band that falls at 980 cm\({}^{-1}\) is due to the contribution of several vibrational modes, that is the C-N-C between two isoindole units, the isoindole deformation and the C-Cl bonds [33]. The Raman band at 1084 cm\({}^{-1}\) is ascribed to C-N, the benzene deformation and the C-Cl bonds [33]. Also, to the C-N bond, the C-Cl bonds, and in this case, the isoindole deformation, is ascribed to the Raman band that falls at 1214 cm\({}^{-1}\). The Raman bands at 1282 cm\({}^{-1}\) and at 1339 cm\({}^{-1}\) are assigned to the C-C bonds and isoindole deformation [33]. The Raman band at 1446 cm\({}^{-1}\) is assigned to several vibrational modes relative to the C-N, C-N-C and C-C bonds. At last, the Raman band at 1538 cm\({}^{-1}\), the most intense of the spectrum, is assigned to C-C and C-N bonds [33]. Figure 10 shows the photograph of the pigment Primary Red Magenta (PRM) (Figure 10a), the optical microscope images of the pigment on wood (Figure 10b) and on glass (Figure 10c) and the Raman spectra collected on the pigment deposited on wood (Figure 10d) and on glass (Figure 10e). PRM pigment is constituted by an organic molecule whose IUPAC name is 5,12-Dihydroquinolino[2,3-b]acridine-7,14-dione and that is usually named as quinacridone. The quinacridone molecular structure is shown in Figure 11.  
Figure 7: Molecular structure of 6,15-Dihydro-5,9,14,18-anthrazinetetrone, named simply as anthrazinetetrone (Indanthrone Blue, IB, pigment). The photograph (Figure 10a) shows the Ruby Red colour of the pigment PRM and the other optical microscope images (Figure 10b,c) show that the morphology of the pigment it is not affected by the substrate. The Raman spectra of PRM show few Raman bands in the range between 150 cm\({}^{-1}\) and 1650 cm\({}^{-1}\) as it is possible to see in Figure 10, because of the presence of luminescence during the acquisition of the spectra. The stronger Raman bands observed in the two Raman spectra of Figure 10 fall at 693 cm\({}^{-1}\), 1316 cm\({}^{-1}\), 1565 cm\({}^{-1}\), 1597 cm\({}^{-1}\) and 1650 cm\({}^{-1}\). The Raman band at 693 cm\({}^{-1}\) is ascribed to the in-plane deformation of the C-C-C bond. The Raman band at 1316 cm\({}^{-1}\) is assigned to the stretching of C-C bond, the Raman band at 1565 cm\({}^{-1}\) is ascribed to the stretching of the C=C bond. The Raman band at 1597 cm\({}^{-1}\) is attributed to the stretching of the C=C and C=O bonds and the Raman band at 1650 cm\({}^{-1}\) is ascribed to the symmetric stretching of the C=O [34]. Figure 8: Photograph of Phthalo Green (PG) pigment (**a**); optical microscope images of PG pigment on wood (**b**) and on glass (**c**) substrates; representative Raman spectra collected with 532 nm laser (blue line) and 633 nm laser (red open circle-line) of PG pigment on wood (**d**) and on glass substrates (**e**). Figure 12 shows the photograph of the pigment Lemon Yellow (LY) (Figure 12a), the optical micrographs of the pigment on wood (Figure 12b) and on glass (Figure 12c), and the Raman spectra collected on the pigment deposited on wood (Figure 12d) and on glass (Figure 12e). The photograph (Figure 12a) shows the yellow colour of the pigment LY and the other optical microscope images (Figure 12b,c) show that the morphology of the pigment is not affected by the substrate. As it can be seen in Figure 12, the Raman spectra of LY on wood and glass substrates are very similar to each other. The more intense Raman bands observed in the spectra are at 1241 cm\({}^{-1}\), 1279 cm\({}^{-1}\), 1318 cm\({}^{-1}\), 1396 cm\({}^{-1}\), 1430 cm\({}^{-1}\), 1500 cm\({}^{-1}\), 1573 cm\({}^{-1}\) and 1622 cm\({}^{-1}\). As reported in Table 1, the composition of Lemon Yellow pigment is benzimidazololone. On the other hand, however, the molecular structure of the pigment shown in Figure 13 is slightly different from benzimidazololone (Figure 13). In fact, the LY pigment is part of a family called Hansa yellow pigments, whose members are also called azo pigments for the presence of N=N bond in their structure (Figure 13).