Infrared absorption spectra of neutron irradiated FZ-Si grown in hydrogen atmosphere have been measured in wavenumber ranges 1800—300 em-1 and 400—200cm-1 by FTIR. The annealing behaviour of stronger absorption bands has been shown. By comparing with spectral results of proton implanted silicon measured by IR and neutron irradiated FZ-Si grown in hydrogen atmosphere measured by DLTS, the possible constructions of H-related centers are discussed.