Radio frequency and microwave spectra for various isotopically substituted water dimers have been studied by molecular beam electric resonance spectroscopy. Resolved radio frequency hyperfine transitions have provided information about the tunneling–rotational levels of water dimer. The microwave spectra have been analyzed with a rigid rotor model to give the following structural information: Roo=2.976 Å (+0.000, −0.030 Å), ϑd=−51(10)°, ϑa=57(10)° and χa=6(20)°. The effects of large amplitude vibrational motion have been estimated and the equilibrium geometry should lie within the above limits. The experimental data is also consistent with χa and φd equal to zero for the equilibrium geometry. The water dimer structure, therefore, has a symmetry plane, a trans configuration, and a linear hydrogen bond within quoted error limits.
The molecular beam electric deflection behavior of (NH3)n, n=1 to 6, has been determined. The ammonia dimer is found to be polar and presumably has a single hydrogen-bond structure. The higher polymers are nonpolar, compatible with cyclic, hydrogen-bonded ring structures.
Tunneling–rotational transitions of water dimer with K=0 have been observed and assigned in the radio frequency and microwave region of the spectrum. Rotational constants and electric dipole moments were obtained from these spectra. The rotational constants show surprisingly large variations with tunneling state for (H2O)2, but not for (D2O)2, indicating that the former species may be following behavior characteristic of a low-barrier tunneling case. A tunneling splitting of 19 526.73 MHz has been observed for water dimer and 1172.23 MHz for the completely deuterated species. The nuclear hyperfine structure of (H2O)2 radio frequency transitions has been assigned and was quite useful for determining the symmetries of the observed states. The nuclear spin–spin coupling constants have been interpreted in terms of the tunneling state of observation and of the water dimer structure.
A new family of six ionenes containing aromatic amide linkages has been synthesized from ready available starting materials at scales up to ∼50 g. These ionene-polyamides are all constitutional isomers and vary only in the regiochemistry of the amide linkages (para, meta) and xylyl linkages (ortho, meta, para) which are present in the polymer backbone. This paper details the synthesis of these ionenes and associated characterizations. Ionene-polyamides exhibit relatively low melting points (∼150 oC) allowing them to be readily processed into films and other objects. These ionene-polyamide materials are being developed for further study as polymer membranes for the separations of gases such as CO2, N2, CH4 and H2.
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