The IR and UV spectra of the silica hollow spheres (SHSs) have been investigated using semi-empirical PM3 method. The calculated results have been compared with those from experiments. A cluster model of porous silica containing up to 36 SiO4 has been proposed to characterize the fine structure of the SHSs. Effects of model size on the spectra have been discussed. The theoretical IR absorption peaks caused by O-Si-O vibration have matched the experimental response well. The UV absorption has been observed to move to larger wavelengths as the number of cluster and the number of configuration interaction (0) increase. The PM3 calculations can assist greatly in analyzing the structure and molecular spectra of complicated materials with special morphologies. (c) 2006 Elsevier Ltd. All rights reserved.