# Spectral Raman Database of Modern Acrylic Paints at 532 nm and 633 nm Laser Excitation Wavelengths
## 3 Results and Discussion
The stronger bands fall at about 484 cm\({}^{-1}\), 680 cm\({}^{-1}\), 748 cm\({}^{-1}\), 954 cm\({}^{-1}\), 1107 cm\({}^{-1}\), 1305 cm\({}^{-1}\), 1453 cm\({}^{-1}\) and 1525 cm\({}^{-1}\). Although phthalocyanine exists in two main allotropic forms, \(\alpha\) (alpha) and \(\beta\) (beta), the PB pigment (Table 1), is made by phthalocyanine \(\alpha\). Thus, the Raman band at 484 cm\({}^{-1}\) is assigned to the A\({}_{\rm 2g}\) symmetry described as the deformation of isoindole; the Raman band at 680 cm\({}^{-1}\) is attributed to the A\({}_{\rm 1g}\) symmetry and it is relative to the breathing mode of nitrogen atoms of the ring. Figure 5 shows a photograph of the pigment Primary--Cyan Blue pigment (PBC) (Figure 5a), optical microscope images of the pigment on wood (Figure 5b) and glass (Figure 5c) and Raman spectra collected with the 532 nm (blue line) and the 633 nm (red open circle-line) on the pigment deposited on wood (Figure 5d) and on glass (Figure 5e). The molecular structure of PBC is phthalocyanine \(\beta\) different from the pigment PB that is a phthalocyanine \(\alpha\). Figure 3: Photograph of Phthalo Blue (PB) pigment (**a**); optical microscope image of PB 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 PB pigment on wood (**d**) and on glass substrates (**e**). The PBC pigment exhibits a dark blue colour (Figure 5a) and the optical microscope images (Figure 5b,c) show that the morphology of the pigment deposited on wood and glass substrates are the same. The substrates do not affect the Raman spectra either. In fact, the spectra shown in Figure 5d,e are similar if collected with the same laser source. The main differences that can be seen between the two kinds of spectra are assigned to the different Resonant Raman effect induced by using the red laser sources with respect to that (Resonant effect) induced by using the green laser source. The main Raman features fall at 591 cm\({}^{-1}\), 677 cm\({}^{-1}\), 744 cm\({}^{-1}\), 1142 cm\({}^{-1}\), 1339 cm\({}^{-1}\), 1451 cm\({}^{-1}\) and 1527 cm\({}^{-1}\). The band assignments are similar to that made above for the PB pigment. The Raman band at 677 cm\({}^{-1}\) is attributed to the A\({}_{\rm 1g}\) symmetry and it is relative to the breathing mode of nitrogen atoms of the ring; the Raman band at 744 cm\({}^{-1}\), is assigned to the B\({}_{\rm 1g}\) symmetry concerning the antisymmetric deformation of the macrocycle. The Raman bands at 954 cm\({}^{-1}\) and 1107 cm\({}^{-1}\) assigned to the B\({}_{\rm 2g}\) symmetry (related to a deformation mode that includes the nitrogen atoms of the ring) and to A\({}_{\rm 1g}\) symmetry (concerning the deformation modes of C-H bonds), respectively, result to be medium bands and not strong as they were in the case of the PB pigment. The Raman band at 1142 cm\({}^{-1}\) is assigned to the breathing of pyrrole group [29]. The Raman band at 1339 cm\({}^{-1}\) is due to the C-C stretching of the same group [29]. The band at 1451 cm\({}^{-1}\) is ascribed to the B\({}_{\rm 2g}\) symmetry described as deformation of the isiondole ring system and, at the end, the band at 1527 cm\({}^{-1}\) is ascribed to the A\({}_{\rm 1g}\) symmetry described as the symmetric motion of all four isiondole groups [27; 30; 31]. Figure 6 shows the photograph of the pigment Indanthrone Blue (IB) (Figure 6a), the optical microscope images of the pigment on wood (Figure 6b) and on glass (Figure 6c) and the Raman spectra collected on the pigment deposited on wood (Figure 6d) and on glass (Figure 6e). The molecular structure of 6,15-Dihydro-5,9,14,18-anthrazinetetrone, the component of IB pigment, is shown in Figure 7.  
The photograph (Figure 6a) shows the very dark blue colour of the pigment IB and the other optical micrographs (Figure 6b,c) show that the morphology of the pigment is not affected by the substrate. Figure 4: Molecular structure of copper phthalocyanine.