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ABSTRACTWe present infrared (IR) absorption spectra over the 800-7800 cm"1 region of cryogenic parahydrogen (pH 2 ) solids doped with H20, D 2 0 and HDO molecules. Analysis of the rovibrational spectra of the isolated H 2 0, D 2 0 and HDO monomers reveals their existence as very slightly hindered rotors, typically showing only 2 to 5 % reductions in rotational constants relative to the gas phase. The nuclear spin conversion (NSC) of metastable J = 1 ortho-H 2 0 (oH20) and para-D 2 0 (pD 2 0) molecules follow first order kinetics, with single exponential decay lifetimes at T = 2.4 K of 1900±100 s, and 860±50 s, respectively. We report without discussion some absorptions of water clusters produced during sample annealing. We report and assign a number of absorptions to oH2-water pairs or "complexes." The main features of the oH 2 -H 2 0 and oH 2 -D 2 0 spectra are explained qualitatively by assuming a semi-rigid C 2 , structure with the oH2 acting as a proton donor to the 0 atom. Surprisingly, NSC of oH 2 -water complexes proceeds at very nearly the same rate as for the corresponding water monomer. We report unassigned spectra of larger (oH2)n-water clusters, and the even more surprising observation of the prolonged survival of 01-20 and pD 2 0 molecules clustered with several o0-2 molecules. We report and assign a number of water dopant-induced IR absorption features of the pH2 host, along with cooperative water-pH 2 transitions in which the vibrational excitation of the pH2 solid is accompanied by a pure rotational transition of the water dopant.