Theoretical Studies on Heavy Metal Sulfides in Solution
'Calculating the stabilities, Raman and UV spectra and acidities of As sulfides in aqueous solution', J. A. Tossell, M. D. Zimmermann and G. R. Helz. Some of the Raman spectra obtained by reacting aqueous As(OH)3 with aqueous bisulfide are shown, taken from Wood, et al. (2002). To interpret these spectra we have carried out an extensive series of calculations, detailed for the case of AsS(SH){sub 2}{sup -} in Table 1 below. By employing state of the art quantum chemical techniques to determine gas-phase harmonic and anharmonic frequencies and solution phase corrections we can accurately match features in the experimental spectrum shown in the top figure. The AsS(SH){sub 2}{sup -}...22 H{sub 2}O nanocluster employed is shown in the lower figure. For this species we have calculated the equilibrium structure and the harmonic vibrational spectrum at the CBSB7 B3LYP level. For the free solute species AsS(SH){sub 2}{sup -} we have carried out a whole series of calculations, evaluating harmonic and anharmonic vibrational frequencies at a number of different quantum mechanical levels. In the spectra below, Fig. 3 and Fig. 5 from Wood, et al. (2002), the features around 700-800 cm{sup -1} are attributed to As-O stretches and those around 350-450 cm{sup -1} to As-S stretches. In the nanocluster an isolated vibrational feature is observed at 425 cm{sup -1}, an As=S stretch, close to the value (415 cm{sup -1}) determined by Wood, et al. (2002). Analysis of the calculated frequencies for AsS(SH){sub 2}{sup -} within a polarizable continuum model yields a similar result. Taking the highest level harmonic results, obtained from a CCSD calculation, and adding anharmonic and PCM corrections at the B3LYP level (designated (3) + (5) - (1) in Table 1) gives a frequency for the intense high frequency As=S stretch within 15 cm{sup -1} of experiment. Although there is still interesting work to be done on the stabilities and the Raman and UV spectra of As sulfides, most of the basic concepts have been worked out and we are therefore proposing to move to a new area, that of humic acids (while continuing our studies complexes formed by As oxides and sulfides, now applied to functional groups present in humic acids).
- Research Organization:
- University of Maryland College Park
- Sponsoring Organization:
- USDOE Advanced Research Projects Agency - Energy (ARPA-E)
- DOE Contract Number:
- FG02-94ER14467
- OSTI ID:
- 1028651
- Report Number(s):
- DOE/FG0294ER14467; TRN: US201203%%188
- Country of Publication:
- United States
- Language:
- English
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