2ND HYDRATION SHELL SINGLE SCATTERING VERSUS FIRST HYDRATION SHELL MULTIPLE-SCATTERING IN M(H2O)(6)(3+) EXAFS SPECTRA

The analysis of the extended X-ray absorption fine structure (EXAFS) s pectra of dilute aqueous solutions (0.1 M) of Cr(NO3)(3) and Rh(NO3)(3 ) was performed using several approaches. Single- and multiple scatter ing (SS and MS) phenomena were taken into account to establish the rel ative importance of their possible contributions to the long distance peak (R approximate to 4 Angstrom). XANADU, FEFF, and FEFFIT codes wer e employed to analyze the data. The first approach considered the sing le-scattering contribution due to the existence of a well-defined seco nd hydration shell around both of the trivalent cations, Cr3+ and Rh3. The second approach evaluated the contribution due to the multiple-s cattering phenomena inside the first hydration shell. Comparison of ex perimental spectra with the calculated ones considering either one or both of the contributions led us to conclude that both contributions w ere significant in the high-R region of the spectra. This study suppor ts our previous hypothesis which states that the second hydration shel l structure can be obtained by EXAFS in these cations, although a quan titative analysis demands the inclusion of multiple-scattering phenome na inside the first hydration shell.