A Fourier-transform spectrometer equipped with a Savart-plate polarization interferometer was developed for observation of weak chemiluminescence and applied to a measurement of emission spectra in the decomposition of hydrogen peroxide with gallic acid and K-3[Fe(CN)(6)]. The band appearing at similar to 580 nm in the chemiluminescence spectrum was assigned to the emission of singlet-oxygen dimol, the peak wavelength being shifted from that observed in the reaction of hydrogen peroxide with sodium hypochlorite, similar to 633 nm. The band intensity was increased with the increasing concentration of K-3[Fe(CN)(6)] up to similar to 100 mM, and thereafter the peak wavelength was shifted from 580 to 700 nm with a decrease in the intensity. (C) 2008 Elsevier B.V. All rights reserved.