Calculation of the visible-UV absorption spectra of hydrogen sulfide, bisulfide, polysulfides, and As and Sb sulfides, in aqueous solutionReportar como inadecuado

Calculation of the visible-UV absorption spectra of hydrogen sulfide, bisulfide, polysulfides, and As and Sb sulfides, in aqueous solution - Descarga este documento en PDF. Documentación en PDF para descargar gratis. Disponible también para leer online.

Geochemical Transactions

, 4:28

First Online: 11 November 2003Received: 06 May 2003Accepted: 28 October 2003


Recently we showed that visible-UV spectra in aqueous solution can be accurately calculated for arsenic III bisulfides, such as AsSH3, AsSH2S and their oligomers. The calculated lowest energy transitions for these species were diagnostic of their protonation and oligomerization state. We here extend these studies to As and Sb oxidation state III and v sulfides and to polysulfides Sn, n = 2–6, the bisulfide anion, SH, hydrogen sulfide, H2S and the sulfanes, SnH2, n = 2–5. Many of these calculations are more difficult than those performed for the Asiii bisulfides, since the As and Sbv species are more acidic and therefore exist as highly charged anions in neutral and basic solutions. In general, small and-or highly charged anions are more difficult to describe computationally than larger, monovalent anions or neutral molecules. We have used both Hartree-Fock based CI Singles and Time-Dependent HF and density functional based TD B3LYP techniques for the calculations of absorption energy and intensity and have used both explicit water molecules and a polarizable continuum to describe the effects of hydration. We correctly reproduce the general trends observed experimentally, with absorption energies increasing from polysulfides to As, Sb sulfides to SH to H2S. As and Sbv species, both monomers and dimers, also absorb at characteristically higher energies than do the analogous As and SbIIIspecies. There is also a small reduction in absorption energy from monomeric to dimeric species, for both As and Sb III and v. The polysufides, on the other hand, show no simple systematic changes in UV spectra with chain length, n, or with protonation state. Our results indicate that for the As and Sb sulfides, the oxidation state, degree of protonation and degree of oligomerization can all be determined from the visible-UV absorption spectrum. We have also calculated the aqueous phase energetics for the reaction of S8 with SH to produce the polysulfides, SnH, n = 2–6. Our results are in excellent agreement with available experimental data, and support the existence of a S6 species.

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Autor: JA Tossell


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