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Raman spectra were collected for synthetic gypsum (CaSO 4 ⋅2H 2 O) powder between 9 and 373 K under atmospheric pressure with special emphasis on the temperature dependence of the OH-stretching modes. The stretching bands of the water molecules in gypsum were found to shift in opposite directions as a result of the different degree of intermolecular hydrogen-bonding between nonequivalent water H atoms and the O atoms of nearby SO 4 ions. The anharmonic parameters of the OH-stretching modes are calculated using the temperature derivatives measured from the present investigation and existing pressure derivatives. These parameters are -4.7 × 10 -6 K -1 and -0.6 × 10 -6 K -1 for the 3407 and 3494 cm -1 bands, respectively. The dehydration of gypsum into γ-CaSO 4 and the subsequent rehydration of γ-CaSO 4 into hemihydrate are clearly identified in the Raman spectra by the observed variation in Raman shifts of the OH and ν 1 (SO 4 ) bands. The latter increases as the mineral becomes increasingly anhydrous (1007 cm -1 in gypsum; 1014 cm -1 in hemihydrate; 1026 cm -1 in γ-CaSO 4 ), which can be used as a fingerprint for the remote detection of these minerals on planetary surfaces.

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.

Raman spectra of alpha-quartz (Qz) grains of various size (250 microm to < 11 microm) and arrangement (individual and aggregated) have been investigated with a combination of confocal Raman and micro-Raman systems. Frequency downshift and line broadening of the 464 cm(-1), v,(Si-O-Si) band are observed in the smallest size group (< 11 microm, both individual grains and aggregates) because of laser-induced heating and are used to estimate the temperature of the sampled region. The intensity ratio of the anti-Stokes to Stokes Raman lines is also used to estimate the vibrational temperature of the samples under different excitation power. The degree of laser-induced heating is more noticeable in the aggregates than in the individual grains with the use of medium-level laser excitation (< or = 150 mW). Heating diminishes with increasing grain size, and it can only be detected in grain aggregates between 11 and 20 microm in diameter using 150 mW excitation. Intensity studies of the v(s)(Si-O-Si) band using individual grains show no noticeable signs of grain size effects. However, grain size effects become an important factor in the study of aggregates in which spectral intensity diminishes with respect to decreasing grain size.