The i.r. spectra of matrix isolated water species—IV. The configuration of the water dimer in argon matrices

Abstract

Frequencies are presented for the water dimer species (H 2O) 2, (D 2O) 2 and dimers involving HDO, in argon matrices. These frequencies correspond to perturbed ν 1, ν 2 and ν 3 modes of the two monomer water units making up the dimer acting as proton donor and acceptor respectively in the hydrogen bonded open dimer configuration. Arguments in support of this interpretation based on experimental data presented in Parts I–III of this series and in this part, are developed. These arguments are based on the following considerations: (a) the number of dimer frequencies observed; (b) the self consistency of the dimer frequencies between the various (H, D) isotopic species; (c) the dimer frequencies in relation to those of the complexes of water with HCl and with (CH 3) 2O; (d) the evidence from the spectra of the isotopically mixed (H, D; 18O, 16O) dimers; (e) some consequences of the preference, evident from the spectra, for HDO to form HOD … O deuterium bonds rather than DOH … O bonds; (f) evidence in the literature. Published arguments and evidence in favour of the cyclic configuration for the water dimer are considered. The apparent lack of a strong band corresponding to the ν 3 mode of the acceptor water molecule in the dimer and in non-rotating monomers, noted in Part II, is discussed.