The X-ray structure, theoretical calculation, Hirshfeld surfaces analysis, IR and Raman spectra of fluoranthene and acenaphthene were reported. Acenaphthene crystallizes in the orthorhombic crystal system and space group P21ma, with crystal parameters a = 7.2053 (9) ?, b = 13.9800 (15) ?, c = 8.2638 (8) ?, Z = 4 and V = 832.41 (16) ?3. In turn, the grown crystals of fluoranthene are in monoclinic system with space group P21/n. The unit cell parameters are a = 18.3490 (2) ?, b = 6.2273 (5) ?, c = 19.8610 (2) ?, ? = 109.787 (13)?, Z = 8 and unit cell volume is 2135.50 (4) ?3. Theoretical calculations of the title compounds isolated molecule have been carried out using DFT at the B3LYP level. The intermolecular interactions in the crystal structure, for both the title PAHs, were analyzed using Hirshfeld surfaces computational method.