The hydrates and deuterates of ferrous sulfate (FeSO₄): a Raman spectroscopic study

Abstract

A comparative analysis has been carried out on the Raman spectra of FeSO 4 ·nH 2 O (n = 1, 4, 7) including the 2 D-analogs. The effects of changing the degrees of hydration have been found from the lattice, SO 4 2− internal, and H 2 O internal modes. Increasing degrees of hydration shift the intense n 1 (SO 4 ) peak to lower wavenumbers and reduce the amount of splitting on the n 3 (SO 4 ) peaks. Some of the water librational bands cause the broadening of the n 4 (SO 4 ) peaks in FeSO 4 ·7H 2 O and the n 2 (SO 4 ) peaks in FeSO 4 ·7D 2 O. The n 2 (H 2 O) band in FeSO 4 ·H 2 O is red-shifted in excess of 100 cm −1 relative to the unperturbed H 2 O band. Between 240 and 190 K and between 140 and 90 K in the spectra of FeSO 4 .4H 2 O, two potential phase transitions have been identified from the changes in the lattice and water-stretching regions. The resolution of the n 1 (H 2 O) and n 3 (H 2 O) bands in FeSO 4 ·4H 2 O and FeSO 4 ·H 2 O also improved sharply at low temperatures. The capability of distinguishing various forms of FeSO 4 hydrates unambiguously makes the Raman technique a potential analytical tool for the identification of sulfate minerals on planetary surfaces.

A comprehensive spectroscopic study of synthetic Fe2+, Fe3+, Mg2+ and Al3+ copiapite by Raman, XRD, LIBS, MIR and vis–NIR

“…The H 2 O molecules at the ten crystallographically distinct sites in copiapite [42,43] give rise to Raman peaks at slightly different wavenumbers, and these H 2 O peaks overlap to form the broad band in the 3000-3700 cm −1 region. This overlap may be removed at lower temperature following the trend reported in the interesting studies by Chio et al [55,56] A diagnostic (sharp) Raman peak of the stretching vibrational mode of (OH) − group occurs near 3522 cm −1 for trivalent copiapite species and near 3528 cm −1 for divalent species as indicated by the dashed line in Fig. 4(a).…”

Time-resolved remote Raman study of minerals under supercritical CO 2 and high temperatures relevant to Venus exploration

“…These changes in the spectrum suggest dehydration of FeSO 4 · 7H 2 O to FeSO 4 · 4H 2 O (rozenite). In the room-temperature micro-Raman spectrum of FeSO 4 · 4H 2 O, n 1 (SO 4 ) is observed at 990 cm −1 (Chio et al 2007). In addition, the Raman lines at 1284 and 1388 cm −1 of the Fermi doublet of CO 2 and weak shoulders at 1265 and 1409 cm −1 are also visible in the spectrum measured under sc-CO 2 .…”

Recent advances in linear and nonlinear Raman spectroscopy II

“…Ibáñez et al 130 studied the hydration and carbonation of monoclinic C 2 S and C 3 S, and Chio et al 131 Sudheer et al 135 reported on the characterization of laser processing of single-crystal natural diamonds using micro-Raman spectroscopy. These workers concluded that the surface quality of single-crystal diamonds is superior when extremely high-peak powers are employed in the laser cutting process.…”