No abstract

ACKNOWLEDGMENTSScience and its advancementdepends heavily on the support of fellow researchers and the labors of scientists long past. Truly no research work is the product of one individual, but rather a team.I would like to take this opportunity to acknowledge a small part of that team.

Nitric acid was allowed to react with NH3 and H20 in an argon matrix environment to permit study of the proton transfer process leading to the ion pairs H30+N03" and NH4+N03~. For concentrations of HN03 that yield primarily the monomer spectrum in a pure argon matrix (i.e., matrix gas to HN03 mole ratios of ~1000), only NH4+N03" forms upon reaction with NH3. However, reaction with H20 under similar conditions yields primarily the 20• 03 complex; the ion pair, H30+N03", is not stabilized until sufficient water of hydration is present in the matrix (~6-10%). Since ion pairs, NH4+N03" and H30+N03", are stable for an extensive range of NH3 or H20 matrix concentrations, it has been possible to observe the effect of variable extents of solvation of these cations on the distortion of the N03~i on by monitoring the p3(e) splitting as a function of matrix composition. Regardless of the degree of solvation the cation and anion are apparently contact paired since the ions are formed in direct contact and it has been shown that, for analogous systems, M+N03" ions are paired in direct contact. The magnitude of the ¡/3(e) splitting ranges from 20 cm"1 for completely ammoniated NH4+N03" and 65 cm"1 for completely hydrated H30+N03" to ~173 cm"1 for the former in a 3% NH3-argon matrix and ~150 cm"1 for the latter in a 6% H20-argon matrix. These data emphasize the severe distortion produced by a bare NH4+ or H30+ ion in contact with an oxyanion, a distortion believed to represent a composite of charge polarization and hydrogen bonding. Finally, work with concentrated H30+N03"-in-glassy-H20 deposits show conclusively that Av3 increases, in such primarily ionic media, as the solvent concentration becomes insufficient for complete hydration of the cations. This observation is compared with differences noted previously between M+N03" ion pairs at high dilution in glassy matrices and the same ion pairs in highly concentrated liquid solutions. Insights to the behavior of concentrated liquid solutions and molten salts follow.

The existing infrared spectroscopic data for the isotopomers of water [H2O, D2O, (HOD)2, and HOD] decoupled in cubic ice at 90 K are reviewed and combined with new results to complete the infrared data for the internal vibrational modes. An assignment of the observed absorption bands, including the perturbed Fermi diads for νs in resonance with 2ν2, that largely follows established views is offered. This assignment is shown to be internally self-consistent by the analysis of the Fermi diads within a single framework based on the simplest representation of the effects of Fermi resonance and using the Burneau–Corset value for the Fermi-interaction parameter appropriate to cubic ice (60 cm−1 for H2O). It is shown that the inclusion of the decoupled-HOD diads significantly lowers the estimated value of νs for H2O and, consequently, allows the downshift of this mode to the observed frequency value (3225 cm−1), through resonance with 2ν2 (where ν2=1735 cm−1), to be closely modeled using the relatively small Fermi-interaction parameter of Burneau and Corset.

Studies of the vibrational spectra of M+N03-ion pairs have been extended by matrix isolation of the vapors of the molten salts in the 400-450°C range in mixed matrices of argon-water and argon-ammonia at 10 K. These vapors are known to be composed of largely monomer ion pairs which in the mixed matrices are observed to associate strongly with the H20 and NH3 molecules. The dominant spectroscopic effect of this association is a progressive reduction in the cation distortion of N03" as measured by the splitting, 3, of the asymmetric stretching mode. This splitting, which, for example, decreases from 260 cm-1 for Li+N03~i n argon to 65 cm-1 in a pure H20 matrix, is observed to decrease sharply to 168 cm-1 for single hydration of the cation and, then, gradually to the pure water matrix value as the percent water in the matrix is increased. This behavior, as well as that for Li+N03~i n mixed argon-ammonia matrices and for K+N03 in argon, matrices mixed with H20 and NH3, is firm evidence that the overall reduction in 3 is primarily the result of cation coordination with the H20 (NH3) molecules with a resultant diffusion of the cation charge density and thus of its polarizing power as reflected in the /3 values. The new data support previous conclusions, based on residual cation effects in the pure H20 and NH3 matrices, that the M+N03~i on pair retains a contact character for all matrix compositions. Thus the ion pair data for glassy H20 and NH3 matrices can be used with considerable confidence to identify contact ion pair features in aqueous and ammonia liquid solution vibrational spectra of nitrates. The matrix data are consistent with recent interpretations of ammonia solution spectra but suggest a new approach to the existing aqueous solution results.