Matrix isolation spectroscopy of H2O, D2O, and HDO in solid parahydrogen

Abstract

We present infrared (IR) absorption spectra over the 800–7800 cm−1 region of cryogenic parahydrogen (pH2) solids doped with H2O, D2O and HDO molecules. Analysis of the rovibrational spectra of the isolated H2O, D2O and HDO monomers reveals their existence as very slightly hindered rotors, typically showing only 2–5% reductions in rotational constants relative to the gas phase. The nuclear spin conversion (NSC) of metastable J=1 ortho-H2O (oH2O) and para-D2O (pD2O) molecules follow first order kinetics, with single exponential decay lifetimes at T=2.4K 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 oH2–H2O and oH2–D2O spectra are explained qualitatively by assuming a semi-rigid C2v structure with the oH2 acting as a proton donor to the O atom. Surprisingly, NSC of oH2–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 oH2O and pD2O molecules clustered with several oH2 molecules. We report and assign a number of water dopant-induced IR absorption features of the pH2 host, along with cooperative water–pH2 transitions in which the vibrational excitation of the pH2 solid is accompanied by a pure rotational transition of the water dopant.