The optimized geometries, infrared spectra and bonding behavior of X~mAl~nH~m(X=Cl，H；n=3,5,7,8,10,12；m=3,4,5,6,) polycyclic comounds were investigated using HF and B3LYP(DFT) method at 6---21G* level for the first time. The structures were compared with correspondingX~mC~2nH~m series compounds such as benzene, napthalene, phenanthrene, pyrene, perylene and coronene. The results show thatX~mAl~nH~m and X~mC~2nH~m share the same geometires; the boud energy of Al------N increases and bond length decreases gradually with R increasing (R is the ratuio of ligand atoms' number and skeleton atoms' number); the ligand X slightly affects the skeleton bond (Al---N or C---C).

Key words: FUSED RING COMPOUNDS, CHEMICAL BONDS, INFRARED SPECTROPHOTOMETRY, BENZENE, NAPHTHALENE, PHENANTHRENE, CONFIGURATION