Matrix isolation infrared spectroscopy has been combined with MP2/6-31+G(d,p) and MP2/aug'-cc-pVTZ calculations to characterize the 1:I hydrogen-bonded complexes between H2O2 and bases containing phosphorus and sulfur as electron pair donor atoms. Most obvious from the spectra of the complexes HOOH:PH3, HOOH: P(CH3)(3), HOOH:SH2, and HOOH:S(CH3)(2) and their deuterated analogues is the shift to lower frequency of the hydrogen-bonded O-H or O-D stretching bands (nu (s)) relative to isolated H2O2 and D2O2. The experimental shifts are in good agreement with the computed shifts. Shifted modes of both H2O2 and base subunits have been observed, along with the band for the intermolecular librational mode of each complex, Comparisons are made between the structures and spectral properties of these complexes and related complexes formed between H2O2 and corresponding N and O bases.